An engine Oil leak may develop from the PCV vent housing on the valve cover and/or the inspection plate on the front of the engine.Google+
Car Problem Reports
Mercedes-Benz E320 Oil May Leak From PCV Vent Housings and Inspection Plates
Mercedes-Benz E320 Problem
Average Mileage: 115,000 mi (110,000 mi - 120,000 mi)
Visitor, 2003 Mercedes-Benz E320, 120,000 mi
Just dried it up
Dealer reported oil leaks in this area. I was allowed to look at the problem and confirmed the condition. It was fixed with a new gasket.