So, what did you do today?

[Casey_SS]

The bolt broke off below the face of the diff, so there is no way I can weld anything unfortunately...

Craig,
I'll certainly use some heat on the housing before I try and drill/spin the bolt out.

Is there loctite on the bolt? If so, you'll want to heat the bolt itself to loosen that stuff up. Probably also want to heat the housing around the bolt to equalize whatever thermal expansion you get from heating the bolt. Without the head, there shouldn't be any torque on the threads aside from any loctite resistance. Maybe try welding the tip of a smaller bolt to it and use that as a handle to spin it out. If it's really down in there, just keep adding tiny spot welds in the center of the bolt until you build it out enough to get to it without accidentally welding it to the case.