I had a similar problem with a bolt on a VW transmission. I tried heat, cold, penetrating oil, wax, and welding a nut on. In the end I drilled it out and ran a tap in the hole to clean out the threads. I wished I had gone ahead and drilled it sooner.
Grind off the end and use a good set of Cobalt (or at least Titanium Nitride) drill bits and make the bolt go away.
