Arthur: As usual, that is a very informative explanation on the starter circuitry.

MBSteve: I think my NSS once went bad due to oil leaking into it and dirt collecting over a period of time. I'm sure this is not a recommended fix, but over the weekend, while you're waiting for your NSS to arrive, you might want to get under there and flood the switch with electrical contact cleaner, then run the gear selector through all positions a few times. I found that this fixed the problem at least for a week or two.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles