Thanks B.S.A.
All things considered, I won’t take any pictures - the space is so small that it would be difficult to really show the problem. Besides, I’ve been busy at the weekend drilling the bolt tail out. Think I might have it now but need to chase the threads to see if I’m in luck or stuck with buying a new bike!
The latter option doesn’t sound too bad mind you - I would go for the red 18" SX - but I do love my trusty old 3.