Robs suggestions have worked for me in the past. Vise grips, slotting the shaft and drilling. Drilling is the most nerve wracking. Patience is key so you don't make it worse. Do tape off the ports so no trash gets in. I did it wrong the first time and spent lots of time getting stuff out of the ports. You need to run a good tap down all the bolt holes after you get the broken one out. The aluminum is soft and the threads deform from over tightening no matter what material the bolt is made of. Also, you have the remains of the thread locker still in their. Agreed that you could put it together and drive it missing one bolt if you needed to. I've driven mine with all the bolts finger tight before. (backed out at the track) Stay calm and patient.

Les

Les