Originally Posted by Tankard
There is a shaft that comes out of the motor that attaches to the flywheel. If that shaft seal leaked, motor oil could get on your clutch. There is also a shaft seal where the shaft comes out of the tranny. If that seal leaked, tranny fluid could get onto your clutch. The clutch sits between the motor and tranny, both of which are lubed with oil. Now if your talking a motorcycle clutch, they are wet clutches which stay lubed with motor oil.
Yes. That shaft you are referring to is the crankshaft.
If it is leaking badly from here, it could be getting on the flywheel and then spun around the bell housing where it would later drip on the clutch assembly, causing it to slip. Unlikely, but probable.