Broken bolt removal is something no one plans for. After years of fighting..I have recently purchased a set of mangled bolt head extractors and have a good set of broken bolt drill and removal extractors. In this case..neither helped.
It is very much a learned skill from having watched a mechanic do it frequently enough.
Buying a nice Tap and Die set for metric bolts (aka our cars) is a wise choice. Last night I used the 8mm 1.25 and 10mm 1.50 taps and the 8mm 1.25 die. Taps clean threaded holes in nuts, manifolds, body mounts..name it. Dies clean the threads on bolts. Both essentially clean threads and have the ability to cut and make threads. This ensures smooth reassembly.
To further illustrate...
Take a cruddy exhaust bolt out and reinstall..hard to deal with both ways and heats up almost getting stuck and breaking.
Same bolt..get it out..run it through the die, cleaning the crud and rust off of it. Tap out the hole doing the same. Now reassembly is simple because it is the same as putting a new bolt into a new nut.
00 Regal GS: All kinds of cool stuff.