Well I found out the real cause of the problem.
After another batch of failed starts at lunch time I followed my nose to the source of the burning smell. I found that the red plastic cover on the positive battery terminal had a melted spot in it. Additionally there was a small spot of melted plastic on the battery case. I checked the main terminal post clamp, it was tight. The clamp has 3 secondary threaded studs which are used to connect the leads. On one of these studs the nut was loose which I assume was causing a bad connection and arcing which was melting the plastic and disrupting current flow to the starter. I just called Phil at Fastlane to cancel my starter order. He was a real Gentleman about it - told me to refuse delivery.

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1990 300CE-24 (Gone but not forgotten)
2002 SLK 32 AMG
2002 ML320 (Gone)
1995 E320 Cabriolet