I did this once and thought I just got lucky. Now I have done it twice and I am very impressed. Occasionally a filler plug gets seized up and breaks off of the rear differential. Then what do you do? I guess you could drill it out and try an extractor? But what I did was weld a bolt to the remaining part of the filler plug that was showing. Then the bolt can be turned with a wrench. It worked like a charm. I really think it has everything to do with the mig welder heating up the plug and breaking it free. Then with the bolt I can get a wrench on there and apply adequate torque. Well any way for what it’s worth, it worked excellently for me 2 times. And only took 5 minuets without putting any drilled metal shavings into the rear. graemlins/hurray.gif graemlins/hurray.gif graemlins/hurray.gif

It works great on any broken bolt, I have used that trick several times even on bolts stuck in aluminum parts. Of course, you need to go carefully with the MIG, or you will melt the aluminum.

As you said, the heat helps a lot to loosen the bolt, and you could probably use the old wax trick (hold a candle aganst the hot bolt and let the wax seep into the thread) to make it work even better. One thing I have learned though is that you need to let it cool off quite a bit before trying to remove the bolt. If it's too hot, it will be weak enough to break again.