Quoted from RoyF:
The standout item to me is the drop in +5v reading at TP2 from 4.97v with J114 disconnected to 4.85v with J114 reconnected. So, something on the CPU board is pulling down the +5v?
I do have a PSU5 on hand so I could easily replace the LM323K when I have the driver board out for inspection, and was thinking of doing that anyway to reduce current draw / heat.
Posting to "close the loop". I pulled the CPU board. All clean on there. Removed the battery holder and installed a coin cell holder, replaced the ROM with 9.4CH. Noticed I had the blue Phillips cap at C31, so I replaced that while I had the board out. Didn't have an axial cap on hand, so instead I used a 100uf 100v radial cap I had from GPE. Reinstalled the CPU. No resulting change in the 5v readings at pin 32 on the game ROM vs. TP2 on the power driver board.
Pulled the driver board and examined it. No cracked solder joints at the headers or at F113. Solder on the LM323K looked good. BR2 and C5 already tested good a few days ago per PinWiki WPC section 6.16.12. Header pins and connectors look good, as expected given the low "on hours" for this game. So, I decided to remove the LM323K and install a PSU5. A simple job, although the PSU5 units I just received in the mail recently differ slightly in appearance from those pictures I have seen posted on Pinside. Notice there are tiny labels screened on the PSU5 for the 2 pins, one says "in" and one says "out". Orient the PSU5 so the "in" pin connects to the back of the driver board trace that goes to BR2 / C5. And as others have suggested, install the PSU5 to the board with the mounting screws first (discard the old nuts and instead use replacement #6 nuts with split washers to avoid a short circuit, and in my case solder had been worked into the head of the screws making it impossible to use a screwdriver on them, so those screws were replaced with new), then go ahead and solder the PSU5 to the board. I now have 5.07v on pin 32 of the game ROM, so all is good! Trimmer pot on the PSU5 can be used to carefully adjust the 5v to where you want it, best done with J114 disconnected for safety reasons.