Well, these cars are known to have that problem (biodegradable wiring harness).
You can do a search in the forum, and read many postings, see pictures and learn the instructions on what problems to look for on the harnesses.
Then you can determine with a relative degree of certainty if the harness is the problem or not.
Another thing that comes to mind is the ignition coil.
IF you are unwilling to take the risk, my suggestion is to bring the car to a good MB technician and have him determine the cause of the problem.
IMHO.

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1999 Porsche 996 Carrera Convertible
1994 420E - SOLD
1986 300E - SOLD, what a car
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