You have to remove the clutch assembly to get at, and see the seal, but if there are oily deposits behind the clutch on the crankcase, the seal may be leaking.  Removing the clutch isn't difficult for a competant mechanic, but you will need proper TKM tools to do this, available from Talko. On the V-clutch the friction material runs on the inner surface of the drum, where any surplus oil/chain lube will gather. The Horstman clutch has it's friction plate at righ angles to the drum, the only contact with the drum being the driving dogs which locate in slots: so any contamination inside the drum won't get on the plate and cause slip. Hope this helps, Dave.
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