What I learned

while working at a Ford dealer about a year ago. This dealer would do the Snap On repair with no guarantee. The tech that did the repair said if done right it was permanent. He also said the real problem was the original spark plugs only had three threads, the replacement plugs were fully threaded and that it was critical to torque them to spec.
That all I know so don't shoot the messenger

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FE's, Thunderbolts and single malt scotch.