Sten

Regarding options Brooksy, there's some good YT vids that might help you out. Intense heat is probably your best bet (1st link), there are other, more "creative" methods though (2nd link) https://www.youtube.com/watch?v=cUlJ5f2-FcQ https://www.youtube.com/watch?v=fqZYgReuywM I'm all for trying to save original threads if at all poss' but sometimes, a threaded insert (helicoil e.t.c) is the only way to go.

As 'Peterrr' mentioned, the tanks are a weak point on these bikes. I read somewhere that using a pressure washer in the vicinity of the filler cap may be partly to blame. Personally, I would take a ride out to a well-stocked breakers, and ask if you could try a few of their tanks to see if anything fits. You can still buy new but obviously, they're very pricey!. Nice Geiger-inspired paint BTW