To start with I wouldn't spend that much money for oil seapage!
I would clean the area with a de-greaser & wait to see if there is a leak that would make it all the way to the floor.
Many times on that engine (M111) the fastening bolts at the front of the head to the front cover work loose, you might try tightening them first. Of course the valve cover has to be removed to check those bolts.
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)