I see the 8mm hole in the spacer, but my 3/8" Allen socket isn't long enough to reach it......
If you can, Bang in a torx (star) bit, just a bit larger than the allen wrench. The torx bit must be attached to a socket and not the L shaped allen style. Though it is not the "right" tool, I have used a palm nailer and a small punch to bang the bit in, where there is not enough room to swing a hammer. I would also add some heat if you can. I like to use a small impact (if there's room) because it gives even strikes. Not a big 1/2 inch impact cranked on high. Good luck