In the process of working my way through the forum contributions and reading of the struggles folk have with broken bolt removal I thought there might be some interest in this vid..? If you are suffering with a broken and recessed bolt/stud, I hope it works for you as well as it seems to have done in the vid.
https://www.youtube.com/watch?v=dJfkCj3FWBs
https://www.youtube.com/watch?v=dJfkCj3FWBs