I'm by no way an expert. Most everything I've learned about my CE, I learned from other members of this fourm and their posts. Just read the archives about the W124 cars (well, technically, the coupe is a C124, but nobody would know what you were talking about). Anyway, the M103 engine has the valve stem guide seal "problem" and the early M104 engines have the head gasket and wiring harness "problem". For the coupes, the '88 and '89 cars have the M103 and post '89 have the M104. That's about all I can add. Anything else, just read old posts. Also, since I got a M103, I only read with passing interest items that relate to the M104. Owners of those cars can give more information about if the head gasket indeed need to be replaced at some semi-regular interval. I could be absolutely wrong about this. They can tell you for sure.