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Everyone's pretty much already said what I was going talk about, but here's a picture of the last stubborn one I removed.
I did soak it with CLR and various penetrating oils to no avail. A little careful heating with the little torch did the trick, but the heat did shatter the glass. The turning tool I used was made from a washer as seen at the bottom of the picture.
After heating it, how much force did it take to get er' loose? I don't want to be dealing with hot parts and still be putting 500footlbs of torque on it, then it snaps off and flies into my eye ball and burns it.
I've never seen one "snap". strip out the slots ,Yes..very common, unscrew slowly, yes again that is common. If your worried about things flying apart, I would wear safety glasses . We can't tell you how much force it will take,unfortunately they release at different torque levels (if at all).