I hav a 2000 yammi yz426. Last week i went riding in wet conditions (lots of clay). When i got home i noticed a leak coming from my drive shaft oil seal. It's the oil seal behind the drive sproket, it leaks after i have ridden it or started it. Anyone know what i have to do to change this. I have the service manual, but it don't tell if i have to take the engine case apart to change it.