The delays in these messages are hilarious. My first reply by email was sent at 8:37 pm EDT. It showed up on the web page maybe an hour later. Even the message sent directly through the web site took half an hour to show up on the web site.
Anyway, if the keys problem is intermittent like that, it's probably a bad connection on CN04. Not tight or corroded or something. Or possibly a bad solder joint where that wire connects to the contact board. As for the G4, A4, A#4, they do not share any common wire. They are all on the last rubber strip of contacts though. Clean the gold contacts on the circuit board and the carbon contacts on the rubber strip. If there is a real problem with the Key Assign Mode switches, that is a whole other matrix on the panel board. Then again it might be just bad connections on CN12 which happens to be right beside CN04. Any blackened traces or other signs of corrosion around those connectors?
Don Backshall