Scott,
I hope that takes care of it for you. I've been fighting the exact same 2 codes for a while now on my 1997 C230 w/118k miles. I've replaced my upstream sensor twice; once with a universal sensor, and the code came back, so I replaced it with an OEM one... and the code still came back. It usually takes a few days for the code to reappear after I clear it. I've also tried cleaning the MAF, but if the code keeps coming back I might try replacing it. I'm running out of possible causes for P0133.

I just finished replacing my downstream sensor to see if that clears up the P0136. That was an absolute pain as I had to lower the exhaust system to squeeze the socket up there to get the sensor loose. I learned from another post that you can lower the back half of your exhaust system easily because it is only held up by hangers.

Charlie