I hear broke stud **** alot. I'll assure you, I can save 80% of all studs and that's being conservative. It's all a matter of technique. Normally you can tell when it's so rusty and brittle it's going to break. The trick is, if you can get it to move 1/2 turn you're home free.
First and foremost, hit it with your favorite lube. WD-40, PB, whatever, but oils works best. Like Liquid Wrench, Your air tool oil that you have handy, or I use my Acetone/ATF mix. Oil is best cuz it doesn't run off as fast. Get a clean new steel nut, preferably hardened if you have one. And run that UP the stud working it back and forth, cleaning the threads. You do all that first. Then try to start working the nut loose, and believe it or not, going in the direction to tighten it first, can help break it loose coming back off. Once you get it moving, working it 1/2 turn back, go forward, full turn back, 1/2 turn forward, another full turn back, 1/2 turn forward, another full turn back. What you doing it allowing the nut to dispose of the rust and **** when you go forward with it and it spits it out the top of the nut, when you're coming down. And you don't have to do this for long since, you already cleaned the threads at the bottom of stud with the clean nut. So once you hit that clean portion of the stud, you've got it made. Trust me, it takes a bit of time, it's a pain in the ass, but it damn sure beats pulling off exhuast manifolds and then drilling out studs. When you replace your nuts, replace them with BRASS nuts instead of steel. Brass being much softer, is more giving, and will strip out instead of tearing up your studs. Just plan on replacing your brass nuts everytime you take them off since they're likely stripped to at least some degree and won't have the holding power they had originally and will have tendency to loosen back up if reused.
