kbaruch1, if you are a DIYer drive your E350 onto ramps, remove the sound encapsulation panel and check for the source of the oil leak. If the oil level sender is leaking, drain the oil before removing the oil level sender so oil doesn't spill from the oil pan. Be sure to use a new O-ring and snug the bolts properly without overtightening them. If the electrical connection of the oil level sender is leaking, then you will need to replace the oil level sender. I should mention that my newest MB vehicle is a 1998 E320, so your E350 has a newer style oil level sender that I have not seen installed ... only in pictures. The concept and approach should be similar though.

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Fred Hoelzle