I would hope there would be a way to test the NSS without having to replace it under suspicion, although it sounds like your is probably the cause of the problem you are having. I had an intermittent no-crank condition on my '98 when I first bought it but it would not be cured by moving the shifter like yours was - mine happened on hot days when the engine bay was hot. At first I thought it might be the NSS but it turned out to be a small black "cube" relay in the right-front electronics box under the hood.

I was able to isolate it to that part first by unplugging relays and trying to start the car...when I found the right one the car would not crank - same as the condition I had experienced. The next time the "no crank" occurred I tapped the relay while my wife held the key in the start position and sure enough the starter began turning.

I replaced that relay (around $15) and never had the problem again. Like I said, it sounds to me like yours is the NSS but I posted this for other W210 owners who might experience a similar no-crank issue.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz