Oil on the clutch can create chatter. yes.
The lining of the disc is a matterial that is designed to resist absorbing oil but it needs to scrape it off of the pressure plateand the flywheel.
The rear crankshaft seal on the Cleveland isn't particularly suseptable to leakage but it does happen.
If it is leaking you don't want this to go on forever. You need to change the seal.
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