How do I replace the fork seals?
The pictures here are from a Suzuki Bandit, but the process is the same for any motorcycle with damper rod forks. For those with cartridge forks (not the 250; it has damper rod forks), this write-up that Brian did on VFR forks will help.
Before you get started on replacing fork seals, you'll need to acquire some replacement items:
Tools that make life a lot easier:
To start, you'll want to "break over", or loosen, all the bolts that will need to be removed. You want to do this BEFORE you get the front end in the air, where the bike will be less stable. You also want to take measurements for how high the forks are in the triples. It's hard to mess up with the 250, since the 250 bottoms out on the handlebar riser, but it's easy to make a mistake with most other bikes. So, measure and write that information down so you can get them reinstalled in the exact same place. You can also use a marker to mark where they go back, but write down the information as well, in case your marks disappear. Taking pictures will also help you get things back together correctly.
Next, get the front end in the air, so you can remove the wheel, fender, brake caliper and then the forks from the triple trees. The wheel only needs to be about 1" off the ground. This is where a purpose-built front end stand comes in handy. Many people use floor jacks with a length of 2x4 between the jack and the headers (this only works if you have the stock center stand). Some people run tie-downs from the rafters to points on the frame and lift it that way. Figure out your method and have it ready.
At this point you may want to consider removing the plugs in the 250 forks if you plan on using the method with a pusher/puller as outlined in the FAQ. It's fairly easy to do after the forks are off the bike by just using a t-handle allen to push down and a dentist's pick to remove the retaining clip.
One thing to be aware of, and make sure you pay heed to, is not letting the brake caliper hang by its hose. This puts undue stress on it and can cause failure. So, hold it up with a tie down, rope, or something similar.
Loosening the damper rod bolt
The next step can go one of 2 ways, depending on the tools you have available to you. If you have a vice, or an impact gun of the electric or air variety, use method 2.
1. Assuming you don't have the above, you'll need to break over the 6mm socket head screw (allen) that holds the damper rod in the fork. This means holding the forks steady and not allowing them to twist. The best way to do this is to leave them in the triples and run the axle through just far enough that it catches on the fork leg you're working on, but not so far that you can't get your allen key/bit into the fork. Then break over the screw, but don't take it out... a simple 1/2 turn will do. It will weep a drop or two of oil.
If all it's doing is spinning the damper rod (you'll be able to feel/hear it spinning in the fork) then you'll need to try one of several methods:
2. If you do have a vice, then it's easier to drain the forks (make sure to pump them to get all the oil out)...
...then put the fork in the vice, with the bottom of the fork facing up. Make sure it's being held by the axle clamp area ONLY, or else you run the risk of damaging your fork legs beyond repair. Sometimes you'll need to pull down on the upper slider (which is now hanging down) to create enough friction on the damper rod for the screw to break free.
Breaking this screw free is the most difficult part of changing fork seals. But don't worry too much. If you live somewhere with even a basic auto shop, they'll be able to get it out for you with minimal hassle. Just make sure to tip the kindly blue collar workers.
Taking the forks apart
What comes out when you remove the 6mm screw is the damper rod and top-out spring (together). This spring is there to provide a 'soft' feel when at the end of the fork travel, instead of just a hard stop. It's also what you're pulling against in the vice to create friction to remove the screw. Be sure to thoroughly clean everything at this point. If you're working with rags and gloves, get fresh ones now. It's important to be clean from here on out.
Next, remove the dust caps (the black seal that's visible when everything's assembled) and retaining clips (just below the seal). Use your putty knife for removing the dust seal - push into the gap and work your way all around, then pop it out. With those gone, you can just slide-hammer the two tubes apart. Slide-hammering is where you just pull them apart with some force. You're trying to use the outer bushing that's attached to the fork tube to push out the inner bushing and oil seal that are held in place on the lower leg with friction.
In the above picture the part labeled 1 is the outer bushing, 2 is the inner bushing, 3 is a washer and 4 is the oil seal. The bushings are copper with a teflon coating that's grey in appearance. Inspect these, and if you can see copper flecks through the teflon, or an obvious wear point, then plan on replacing the bushings. Also, an obvious wear point going up and down tends to mean a bent fork leg (upper or lower, depending on the bushing) and is a likely cause for the leaky fork seals.
Next is a close-up of the forks. Note the rust pitting. These forks had a fair bit, but it was all above where the oil seal slides.
You also want to be on watch for dings in the fork tubes from rocks. This is the reason 90% of fork seals leak in the first place. Shown below is a bad one - bad enough that the forks will always leak until that leg is replaced. See here for more information.
For a short-term fix, that may or may not last, you can sand the dings down with sandpaper. You want to create a cross-hatch on the entire length of the fork that the oil seal slides over. This will knock down the edges on the rock dings, clean off imperfections, and generally allow the new fork seals to have a chance at lasting more than a week. Sorry, no pictures of this process, but see here for more details.
This one still weeped oil a bit, even after sanding. You should really replace the fork leg if it still leaks after sanding down the high spots.
Installing the new seals
This sleeve (photo below) fits in the bottom of the tube; it must be re-inserted in the lower leg with the fork tube BEFORE hammering in the new seal, unlike the damper rod, which gets dropped in later.
Below is the oil seal - top first, then bottom. The "solid" side always goes up; otherwise, there would be nothing to push a seal driver against when installing new seals:
Lube the inside of the seal with some waterproof grease, such as Bel-Ray Waterproof Grease, though just rubbing some fresh fork oil on them should do the trick as well. Be VERY CAREFUL installing them back onto the fork, as you can easily catch an edge and tear the new seal. A piece of cling-wrap over the mouth of the fork leg may help (or part of a sandwich bag, with a corner up). Also, make sure you have the inner bushing and washer in place before putting on the oil seal. No worries if you forget; just take off the outer bushing and put the washer and inner bushing on.
Put your newly refinished upper leg into the thoroughly cleaned lower leg, push the seal and bushings down to where they belong, and then put the old fork seal on top of all of that. It is preferred to beat on the old seal and let it push the new seal into place. There's less chance of tearing something up with the PVC pipe. Next, put your seal driver on the fork and hammer everything into place. This one has a rip down the length of the PVC because it was slightly small:
This can sometimes take quite a bit of hammering. The end result you're looking for is that the seal is pushed past the groove where the retaining clip fits (as seen on the left and right of the upper tube):
Then, use the putty knife to remove the old fork seal after you've used it to bang in the new one. There isn't much at all exposed above the lower leg to grip it and lift it off - just push into the old seal and give it a twist.
Put the retaining clip and dust seal back on. With those together, drop the damper rod back into the fork, then put the fork spring on top of it. With the fork spring and spacer back in the fork, lay the fork on a work table and push the open end into the wall. This will put enough pressure on the damper rod to hold it solid while installing the screw. You can also do this with the fork inverted; just make sure to use something to cushion the end (carpet, piece of wood, whatever). And do not, under any circumstance, put thread locker/loctite on that screw... or any other chemical, for that matter. It's just asking for trouble, and it will make the forks nearly impossible to disassemble in the future. Again, no picture.
The last step is to fill the forks with oil. You do this with the fork fully collapsed (pushed together as much as possible), and the spring/spacer left out. If you have GVE (Gold Valve Emulators), those should be in the fork. Pour in close to the right amount of oil and pump the fork up and down to bleed as much air as possible out of the damping rod. The air will feel like the fork is skipping a little... It should only take about 4 pumps. The best method for measuring fork oil is to go by measurement down from the top. Measuring fork oil volume only can leave the forks way off.
Fork oil level is supposedly 226mm +-2, but there is some disagreement about that. This shows a 6" machinist's ruler being used to measure oil level. You can use a piece of dowel with the right depth marked on it, a large syringe with some hose, marked at the right level (to suck out the excess... easier if you have more than 2 hands), or any other method where you can get consistent results.
All the oil level controls is the air spring (or volume of air trapped in the top of the forks) and all that does is control how easily the forks bottom. Since most riders on this forum will never actually bottom out a pair of forks, it's not an issue. So, just go with the recommended level from the link above. If you become a racer, then you can play with the level.
Past that, just drop in the spring, washer, and spacer, and reinstall the plugs/caps and retaining ring. Putting the forks back on the bike is the reverse of removing them. Pay heed to your height measurements.
All in all, this is a task that's easier than doing the valves. Most shops will charge about $125 if you bring the forks in. You should be able to do the whole process in a couple of hours if you're well prepared.
Hint: Sand off the bug guts and the rock dings periodically while the forks are still on the bike. This will help prolong the life of the seals. You want to be as clean as possible when doing this, obviously.
This writeup is on an SV650, but it has lots of pictures and may give you more of an idea of what you're getting into. Note that she also says that it's a little complicated but not difficult.