The chances of getting so many bad used sensors is impossible. Its either intermittent wiring issues or more than likely coolant leaking on it. The coolant leak could be a small drip that evaporates and isnt visible. Ive never had a problem with the pump o rings failing only weeping out of the hole. Then again I change my pumps and crank sensors at 70 to 100k. Ive also never had issues with crank sensors failing and even sold a used one recently that works fine. Ive had a sho on the road since 02 and they were my daily during most of that time until recently.