Patience. Take your time. Lots of good advice so far. Haven’t used Kroil, sounds amazing . The shipyard at Newport News used to use PB Blaster which is decent.
Another method would be to drill out the “head” of the Allen bolt. Collapse the head of the bolt, remove block, use pliers to remove shank of bolt. This requires a good drill bit and a steady hand.
I have used carbide deburring bits in die grinders to accomplish the same.
Good luck! Let us know what works.
I most definitely will, and I'll take pics to give all my good Freeper friends a better idea of what I was dealing with. Many thanks!