My 1990 M103 had oil leaking in the same area you described plus some running down the back of the engine. Had a safety inspection at the local MB dealership and they called me back to see the leaks from under the car. The mechanic told me the very same thing you were told. No oil in the coolant, no oil consumption. I asked about a leak from the valve cover. He said no, head gasket failure. Very close inspection by me later showed oil clearly leaking from under the valve cover on the passanger side (between the exhaust header pipes) as well as from the back of the cover. Less than $10 for a new gasket, removal of the cover plus thorough cleaning of all areas produced zero leaks for the past two years! I still have a very slight leak at the front timing chain cover - most do. It has already been re-sealed once by the dealer 10 years ago but this time I will do it myself. Think I can do a more effective job. I expect to have to do a head gasket job eventually, but not before it's time. Currently at 97K. Hope it hold out for another 20-30K, then I won't feel bad about a complete valve job.