Hi Damien

can be a lot of things, most beyond my expertise!  Did the sustain work before the fault occurred? Or before you replaced the caps?

One simple thing you can try is reseating the connector on the sound board and J3 on the solenoid driver board.  I once tried all sorts of things on my Paragon sound board when it was playing up only to 'fix' the issue by reseating J3 on the SBD

good luck
Ian