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 ML350 Oil May Leak From PCV Vent Housings and Inspection Plates
Mercedes-Benz ML350 Problem
Average Mileage: 101,117 mi (41,000 mi - 170,000 mi)
Visitor, 2007 Mercedes-Benz ML350, 170,000 mi
Oil leak had to replace breather part on back of head
Mine was described as "valve cover breather" both right and left leak oil. Didn't trust the dealership, Barrier (after ongoing failed steering fluid leak repairs) so I went to their ex-employees at Mercedes Garage. They replaces L&R valve cover gaskets, rebuilt upper chambers, replaced breather hoses."