My clutch on my 85 944 slips a little in 4th gear up hills. It only slips when the engine is warmed up though, like 20 miles into a drive. There is also an oil leak in the rear of the engine. Is it possible that oil is dripping onto the clutch plate and making it slip?

 

Yep. Rear main seal may be leaking.

 

time for a rear main seal and a clutch disk.