THere was a fellow on my tool route that would travel around to the shops that had broken studs in heads. He had a small tig welder. He could weld to the broken stud even if it was broken off below the surface, build up weld, and eventually weld a washer and nut so the fastener could be removed. Years ago he was getting $100 a removal. He had very few failures. I have heard of that being done with a wire welder as well but the tig gun is so much smaller in those hard to get places.