I have a 1998 E300TD and I lost my gas cap. I went to the local Mercedes dealership's parts department and bought a replacement. It fit very snug and a few days later I tried to remove it and it wouldn't come off. I eventually got it off with a pair of pliers and went back to the dealer. The parts people didn't know why I would have a problem with the cap so they sent me to service. The service rep told me they had 3 prior problems with new gas cap replacements on E series cars earlier than 1999 and I would have to go to a junkyard for a replacement. He told me that they even tried to file down the inside phlanges of the new gas cap on the other E series they worked on. I wasn't satisfied with that so I went back to parts and a manager there talked to the service manager and neither had any knowledge of any prior gas cap problems. The service manager said the inner lip of the place where the cap fits into is bent and that is why it wouldn't work. Personally I believe the new cap bent the inner lip when I tried to get it off. They offered to fix it for me but I didn't have the time nor did I feel like paying them to fix a problem the new cap may have caused. They also told me they had no idea where that first service person got his information. I know this sounds minor but I'm driving around with a broken cap that doesn't seal and there are diesel fumes coming in the car. Has anyone ever had similar problems with a new cap. Thanks.
Jon

 

PRoblem solved with a $5 gas cap from autozone. It is all metal except for the rubber seal, not like the mostly crappy plastic one for $15 from the dealer. There is definately a design flaw there!

Jon