I have a 1999 E320 (W210 M112[?]) with the CEL lit and codes P0156 and P0161 showing on the reader. I have found several threads confirming that this is the driver's side rear O2 sensor, and thanks to FastLane, I even found a picture of the offending part.

Unfortunately, I have not been able to find any information on how to actually change the sensor. I looked along the sides of the engine last night and can't for the life of me figure out how I would get my hand down there, let alone with a wrench and then turn the wrench.

Any help is greatly appreciated.