For a while, I used PB40, use it for general stuff now. I started using heat and melting candle wax into the threads (like the beeswax above), tighten just slightly, then loosen and a tad more wax into the threads and have yet to break on off or damage the threads. Downside is it only works if you can get the candle to threads. If it's in a blind hole with no threads showing, not much I've had luck with other that heat the wee out of area around offending fastener, then place some dry ice on head of bolt before trying to tighten, then loosen. Usually end up snapping the bolt off and drilling it at that point.
