Are you getting any error codes from the computer? I have a '93 300E with the same problem as you are describing and have yet to nail it down. I noticed with mine that if you have just turned the car off after driving a ways, it can be extremely hard to get it to fire back up. Have you noticed anything else strange that might help lead to your problem? Checking the pressure on the fuel rail is a good idea, and it should be around 60 psi I believe. You may also want to see if there is someone near you that can check your ETA, and you probably want to check the wiring on it yourself. It has the same degrading wire as so much of the car had, and isn't replaced by changing out the upper or lower harnesses. Hoping you have a trouble code that helps lead you to your solution.