100000000% agree with this. I just spent a couple days salvaging my muffler assembly as an 02 sensor stud broke off in the cast iron welded adapter in the exhaust tube. No amount of torch heat would get the stud hot enough as the exhaust tube would immediately cool the area too fast to be able to use my stud extractor. After a couple failed attempts, the welded nut backed out the broken stud like I just installed a brand new bolt with antiseize. This is the way.The best solution at this point is to weld nuts to the broken bolts. The heat generated by welding, passed through the bolt, will breakdown the rust bond between the broken bolt and the original nut integrated into the frame.