Thanks for the advise, I did have an idea to tap a little m3 hole through the stud plate and bolt the mirror in with a little hole through the inner plastic side beside the glass mirror, but this may have stopped the mirror moving free, and gerarally felt like a bit of a hack... so I caved and bought another stud plate. If this gives me anymore grief though I may reach for the epoxy in a rage!
Lastly, I take it there are nuts on the back of the screws holding stud plate into the fairing. I'm guessing I'm going to have to remove the rubber inserts where the fuel gauge is to get to the back of that. I'm learning how much of a faff it is to repair bikes with fairing! Oh well.
Cheers. Jon