I've been reading some of the threads regarding difficulty with starting on the 300e's . Mine also is difficult to start, so I tried one of the tips mentioned. I turned the key to the on position ,waited 10 seconds and the car starts first time. I suspect the there is a fuel pressure problem on start-up. Some people have mentioned a valve that stop the fuel from backing up, but MB dealer had no clue. Does anyone know what part number I should be ordering or have a picture that I could show the dealer. I have a 1991 300e 4-Matic.

You probably mean the fuel pump check valve. Try 000 090 13 10. You'll need one for each of 2 pumps unless you know which one is bad.

Sixto
95 S420
87 300SDL