Rear disc mot failure

[GrahamB]

Bit late for what I'm about to say in this case but I swear by this method if the bolt heads start to chew up. I hammer a multi spline bit in the slightly damaged bolt head where an alan key fitting should go. Forget the size but if it grips nicely but won't push in then that's the one! Relevant socket & use a breaker bar. Have to tap the bit left & right after to get it out the bolt head after but much better than all the hassle you are having now!
I would have to say mig weld a nut on the stud now as a first attempt.