I just cleaned the sending fuel guage sending unit in my 1991 300D 2.5 and I wanted to pass along that the unit is removed through the trunk, not under the back seat, for this particular model. I started by removing the rear seats and removed the plastic 6 inch body plug, but nothing was there aside from the tank itself. I removed the carpeting in the trunk and these she was. I cleaned the tube with brake cleaner to remove all that gooey black stuff, then I soaked the tube in ATF. I put it all back together and now my fuel guage does not dance around like a pin ball flipper.