It's become fact for me that not all "fix-it" plans work when it comes to broken bolts. Most people swear by welding a nut on, others soak the bolts in PB blaster or something similar for days before taking an impact gun and zipping them out, that usually works. Welding a nut will work in most situations, but not all. Our GS550E had two broken exhaust stud bolts, and welding the nut only made it worse. Any time I tried welding a threaded nut on, letting it cool, heating it up, and wrenching it out, would only snap off additional threads and the nut on the bolts, each time leaving less and less space to use that method.
The easiest fix? We spent like $50 on a decent/pretty nice and complete tap and die set. We simply drilled out the two bolts, and re-tapped the head. This fixed our issue in an hour, and the exhaust and everything was back together and on the bike. As the others mentioned though, just make damn sure that you're in the center of the bolt when you start drilling, because if you end up tapping the bolt to the left or right of the left-over broken stud, and not in the center, even an 1/8" is enough to cause the collars to not meet up and bolt up crooked or stressed.
P.S. I'm not saying extractors don't work, but Any time i've used an extraction kit on a bolt like an exhaust stud that's broken, they never worked for me. They would thread in and twist so much, that I was worried it was going to break the extractor in the bolt, which makes the issue twice as hard now to fix if that happens.
