I have run into this problem many times. The factory uses a very tough thread locker on these bolts. The solution is use a large blunt heavy drift and a heavy hammer, ued directly on the head of the bolt, to break the threads loose. The head of the bolt will deform inward from the impact, but you can drive the allen socket into the head and then loosen. The rounded out socket in the bolt head will deform inward from the heavy blows and will allow the allen tool to grip again so that the bolt can be removed. Replace the damaged bolts during re-assembly.