Noticed a coolant leak from the thermostat area and thought the bolt closest to the engine holding the thermostat was loose from vibration, etc, so I tried to tighten it. The bolt "slipped" past the point of tightness and became loose. So, figured the bolt might be stripped, pulled it out looked fine. Replaced it with a new bolt, same thing happened: got to a certain point of tightness then loosened up. Now I am figuring that the housing for the bolt is stripped. Was looking at going to the next size bolt, rebore and rethread the housing. Anything I should or should not do before I proceed? What is the best way to rethread? Thanks!