LOL, after all that C1 had already been replaced by a 4.7uF cap!

Anyway, turned out to be a (fairly obvious) dry joint on one of the flyback pins. I didnt end up replacing anything, although there was some shrinkage of the plastic around some of the caps (but the caps themselves hadnt bubbled up on top) - so maybe a repair for me at some later date. I did however freshen up all the joints you mentioned.

Cheers,

-Gav.