I second that, don't use anything but propane to heat aluminium. Even then it should only take a few seconds of heat to make it expand enough to break the plug loose. I used a little heat when replacing the races in the T5 in my Mustang and it only took about 5-6 seconds worth of heat from a propane torch for the race to seat with a little added persuation from a rubber mallet. The job would have normally called for using a press to install the new race.

 

I would not expect it to work on a filler bolt in an trany, I had the same problem on my truck, I tried heat, penitrating oil, cheater pipe, i finally broke the plug head and then drilled and retapped. best i could figure is either someone cross threaded it or used an impact on it. It should not get corrosion on steel threads in an aluminum housing filled with oil.