If you can find a replacement, then I'd go after it with a tool specifically designed to remove screws/bolts with messed up heads. I know Sears sells them, and I'm sure other places do also. But they will finish ruining an already messed up head. If you can't find a replacement, then I don't know what to tell you. Numrich has the part listed....no idea if it's an original or not.

John