Sounds to me that the issue could still be J4 as the machine played well for four games. You say the pins have been replaced - what about the connector itself ? You should unsolder the old one and replace it. Pins and connectors should be done together.
Failing that - reseat all the socketed ICs. Be CAREFUL when removing the 5101, as it is prone to static. Clean all other connectors - "dark" color is not a sign of healthy connectors.
Failing that - could very well be a PIA - they can be swapped over.
