OK - well two lovely new mirrors arrived from Busters and the left hand one fits perfectly on a 10mm thread.

The right hand one is - well the mount is just odd.

It looks like an original mount, but it's as if there is some kind of half inch by 3/4 inch stand off screwed into it. The base of the "standoff" has a nut on it.

I guess I need to find my digital camera and take a picture.

It looks like it has a thread inside the standoff but it may be around 8mm??

I had a go at trying to unscrew it but it all looks a bit fragile and I didn't want to bugger up the master brake cylinder.

Would anyone with a Mk3 mind posting a pick of what the right hand side (sitting on the bike) mirror mount looks like???

it sounds like its just an adaptor to take 8mm thread mate. They are quite common. Just unscrew the thing. Std thread is 10mm.

Keep hold of it in a tin though, its handy to have in the future.

Thanks - time to break out the WD40 and the FBS then.

Barman - a pint for Vilguy, and one for yourself.

Appropriate use of the FBS got that off. Marvellous. Just didn't want to crunch up the ali housing up that end.