spaz

I have a 96 xv535 that's leaking at the clutch shaft seal where it enters the case behind the rear cylinder. Local yamaha shop said they have never seen one leak there before. I've checked the crankcase breather and it's clear. Does anyone know what caused the leak and do I have to pull rear cylinder to change the seal. Also I noticed that the aftermarket clutch kits note that kits are not for full synthetic oil. I've been running amsoil for the last 20,000 miles. Bike has 25,000 miles.