I had the professionals at autozone give me a free engine diagnostic and it said I had a major evap leak, so they sold me all four o2 sensors and installed them free in their parking lot. I gave the guy a tip for installing them for me, anyways the light is back on and it says it's the dfpe, anyone ever change one on a MB and how much does it cost? I dont want to take it to a shop and get ripped off by their 35 dollars an hour rate.