OP

Quoted from filthyPierre:

The plastic opto interruptors or whatever they're called that actuate with the flipper buttons - the left one has a copper thing over it that acts like a return spring, while the right one doesn't. Should it?

OP

Quoted from filthyPierre:

@pauly - nothing. The buttons are the sprung type, there is a spring in the button that returns it to the fully out position. The black interruptor just goes back on its own... so now that I've realised the interruptor should have a spring it's possible that the lack of spring could be causing the "sticking" problem, if the interruptor doesn't return as quickly as it should. It will be the first thing I order tonight.
@bobukcat - thanks, I've found some black ones at Marco Spec, will order them tonight along with some new springs.
Thanks for the help, will update when I've gotten the parts.
Cheers,
Pete