Swapping exhaust one of the nuts/studs was seriously, seriously seized; Nut sheared off so I tried plus gas releasing fluid, blowtorch, then 2 types of stud extractor. It finally moved but 😫a chunk of the 'boss' that receives the stud broke off. There is just about enough thread left at the bottom of the hole to take the replacement stud, and because the exhaust flange holds the stud straight, it is also getting purchase on the remaining threads on the broken section. However I am very nervous about applying serious torque to the nut/stud. At the moment it is not blowing, but I would like a bit more security. I have the piece that fell off; can it be welded back and tapped, or is there an epoxy repair putty that will withstand the heat?