I just encountered the same problem and the San Antonio MB dealer quote me $3,250 to replace the sensor, ME, wiring harness and O2 sensor, almost sounds like they can a canned answer to this problem. I am really puzzled how oil can travel through a two wire harness back to the ME when it's up hill from the sensor, something does not seem right. I will go back to the dealer and get the fault code or codes and take it to a shop that has been repairing MB for years. I will definitely share your expertise and advice with him. Thanks for sharing your experience with us.