I just went through this problem on the 95S. Oil was leaking from the valve cover seals (around spark plugs) and dripped from the back of the cover (passenger side, at gasket level) onto the exhaust manifold. Was worse idling after a run.

Changed the valve cover gasket (including sparkplug gaskets), rebuttoned it up and now no more leaking oil/smell.

Take a good look at the back of the engine. I had to swipe it with my hand to find the trace of oil leaking.

Ron

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1995 E320 -171k-km
1995 S420 -333k-km