If it's measuring over 12 after sitting. I am still leaning towards high resistance in the battery cable running to the starter. Measure voltage at the starter when trying to crank after sitting over night.

http://www.aa1car.com/library/voltage_drop_testing.htm

If you think you are having parasitic drain:
http://www.aa1car.com/library/battery_runs_down.htm

Had an old car once. It would leave you stranded but not consistently. Eventfully I cut into the insulation on the battery cable and saw lots of corrosion internally, not at the ends. High resistance, 12v not getting to the starter.
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