I've got the exact same thing going on with my 92 300E. Took it back to the mechanic and dropped the pan. Put another gasket on it and re-affixed. Kept leaking. So, after some discussion I'm going to try solving it this week-end. It appears that the middle bolt on the right side may not be gripping the way it should due to some sort of "flaw" in the pan. Could be that the lip is bent or that the hole through which the bolt slides has somehow enlarged itself. The leak is definitely coming from this particular area. I'll post once I've looked at it Saturday morning.