Yeah, deoxit for starters and those metal clips help way more than you'd think. De-casing the B board and connecting it directly to the A will also help with the connection. Good luck!
Deoxit might help for sure, but you might have some improperly seated roms and/or a corrupt or failing rom. From my meager experience diagnosing cps2 issues
2mm or even 1.75mm would be much better, I think there is a smidge of play in the OEM ones
The screw holes I did not test because the frame I'll be mounting this in is not standard so I'll need to drill some fresh ones.