God dammit, I wish I had seen this thread about two weeks ago. I had the exact same problem, the bolt was just spinning and wouldn't come out. I ended up ripping the fucking thing out, along with the plastic that the nut sits in. In the process of ripping it out, I cracked the fender a bit where it mounts on and now there is also a hole that goes directly into the tank. So angry...
I ended up buying a used tank on eBay, BansheeCJ3 happened to be the seller.
If anyone can give me some pointers as to what I should do with the broken tank, that'd be great.
Otherwise it is headed for the dumpster... ::