[175K911]

I had a similar problem with one of the passenger side bolts on my car, looks like someone really cranked down on the allen bolt at one time and instead of an allen it was now a big round cavity. I tightly clamped a pair of my needle nose ViceGrips to the head, one jay inside the allen and the other outside. Then put a screwdriver blace through the jaws for leverage and gave it a wack with my rubber mallet to break it free. Took a few tried but came free. I used needle nose for more movement when turning the head of the bolt, coulcn't get the regular ones to fit in there and still allow room to turn.

I sourced replacement grade 10.9 allen bolts from my local Ace Hardware of all places. Be careful of what you put in for bolts, I think the factory ones are grade 8.8 so you don't want to use cheap unrated bolts.