1988 560sl misfire

I have my eyes set on a local 1988 560sl for sale. The car starts a little slower than I think it should and has a very rough idle. The seller indicated that oil is leaking onto a spark plug and causing it to misfire. Any ideas on a price range and/or amount of hours parts and labor to fix this problem? What is the problem anyway? Any feedback is appreciated.

First off, I think you should be concerned about this 'little oil leak' that finds it's way to the spark plug. Just on the surface, this does not sound good at all. Any oil in the cylinder should be below the oil control ring, not above it toward the spark plug. Secondly, slow start could be attributed to easily fixable items. But take a concern toward the oil on spark plug problem first.