Here is my thoughts on this FUBAR; use a 6 point box, ground down thin enough to fit; a 12 point will slip/strip on the hex. PB blaster, a pin punch and a hammer hit the flats of the bolt you can see/get to, the action will wiggle the bolt back and forth, breaking the rust bond, PB blaster some more, try the wrench. You don't have hit the punch with a kill shot, just a solid bump.
