OK, first real problem - potentially. Everything else up until now has been an easy fix (resolder jobs and realigning switches).
LHS flipper is not firing correctly, and 'chatters' (repeatedly fires the coil, hits EOS, fires again). In the switch test the flipper switch when held in is basically going on and off rapidly.
So far I have attempted to clean the optos; might still take the board out and do it properly, but I have a sneaking suspicion the problem is somewhere else down the line.
Any suggestions of what else to check out? (The manual is available for download at IPDB if you are interested.)