I would have to venture on a new idea. I had a similar issue with my 1992 300SE and it turned out to be a relay with the alarm system that went bad. When the alarm is activated, all power is cut off to the fuel pump. If you try to start the car, it will simply turn over, but not start.

Also, try disconnecting and re-connecting the battery. That worked for me initially before the relay went bad all together.

I hope this helps!

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