RH Mirror problem

I can't remove my RH mirror because the screw/bolt just spins. This has also stopped me from be able to tighten the bolt and because of this I get a horrible rattle from that area between 3500 - 4200rpm which stops if I squeeze the matte black dash against the fairing. The mirror doesn't move and nothing flaps about it's just the dash isn't pressed snugly against the fairing so makes the rattle. Any ideas on how I can sort this out, at least be able to tighten the bolt?

[Dipper]

Have you tried pulling on the mirror as you turn the screw, or you could try an electric impact driver to unscrew it.

I've tried all sorts, even had the garage spend 30 mins trying to get it off when it was in for it's full service. Didn't ask them to but forgot to tell them it doesn't come off.

[andrewsmith]

Sounds like the threads gone on the retaining bolt or mirror screw.
I think you can back the bolt out with the retaining bolt in place, failing that you should be able to squeeze a close quarter hacksaw in and cut the head off

I don't think the threads are messed up. It's the retaining nut inside that has come loose so just spins with the bolt. I can pry the plastics apart just enough to get a glimpse inside but not enough to fit any type of tool in there. I just want to be able to tighten it up to stop it rattling. I'll have another look tomorrow.