I'll vote for some possible locktite usage. Heat will help break it down. Heat it up, keep it reasonable, and then let it cool. It may be enough to release the locktite.

The extension broke because of the pipe on the breaker bar. 1/2" stuff is tough, generally, but adding that extension easily multiplied the torque on the system. As long as the socket is tight, the bolt won't round and the weakest link breaks (the exension). Now, don't get me wrong, I abuse tools like the next guy, but it is good to know what the limits are and how likely it is that something is going to break.

Good Luck,
Michael