I would add to the list:

Die-electric grease (auto parts stores carry it). Once you've cleaned the contacts with one of the above products, apply a bit of the grease to the same contacts. Especially those that are exposed to the environment.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car