My son's '96 KDX220 is leaking pretty heavily around the primary sprocket shaft. The schematics I have seen show a collar and two O-rings around the shaft. Can these be replaced withour splitting the case?
Remove the sprocket. Use a seal puller and pull the seal around the output shaft out. The collar should slide right out and the o-rings should be exposed. Most likely you'll have to replace the collar, seal and o-rings to get it to stop leaking. Make sure you grease the seal when you reinstall it.