Go with what Andy says. I'd soak it with Kano Kroil (the orange can) for a couple days, spray it every day. Then drill a hole in the bolt, it doesn't have to be perfect but about 1/4-1/2" deep and use an easy out. Or you can drill it with a left hand drill bit also. I've seen them pull the bolt out as you're drilling the hole since it heats up the bolt from the inside and makes it easier to come out.