the drilling out of broken bolts is one of the most difficult arts to master. There is a reason a master machinist makes a very good living. This is one of them. On a BMW, assume it has lock tight. I have several wire stands for my heat gun, so it can sit and do its thing while I take a break and walk around muttering random obscenities about German bikes, German engineers and German parts in general.. When the part is hot, they screw right out.
Then when it is back together, the Koolaid is so good!