An update to this thread:
http://www.ukclimbing.com/forums/t.php?n=612790
(Which has now been archived, otherwise I'd post this there.)
In case anyone is interested, I took my fuel tank and fairing to F1 in Cudworth, as recommended by John Simpson. In the end I got them to repair the broken mudguard and repaint that as well.
I've just been over to pick them up this afternoon, and I'm very impressed. They've done an excellent job of the paintwork, and I can't see or feel where the cracks in the mudguard were. The paint is probably better than the original finish when the bikes were new. Only problem now is that the replacement bits are going to make the rest of the bike(s) look shabby. ;O)
Thanks very much John, I definitely owe you a pint for the tip. (And so does your mate Chris, I reckon.)
