Handling is limited by soldered in keyboard connector which is mono strand wiring that breaks every time I flip the board over and has to be resoldered each time the motherboard is taken out.
My intuition tells me there may be a failing solder joint on the motherboard somewhere, due to the intermittent nature of the keyboard errors. But the CMOS battery failure is now a hard, always-on, failure. In the past, taking it apart and putting together again with a new battery used to fix it for a few months.
Most systems detect a keyboard connection by monitoring the current flow
through the connector. To trick it, simple wire a 10kohm resistor between GND (pin 4) and +5V (pin 5). This is on a standard PC/AT style connector (the larger 5 pin one).