I went ahead and ordered a pinscore in the hopes that it solves the problem. It should, but I noticed some burn marks on the main board near the connector for P3/4. I plugged P1 into it in a round about way since they aren't meant to be swapped and there was data flowing (garbage on P1) so I know something is coming through it.
I also installed an off-board battery holder over the weekend. Works like a charm. I'm looking forward to the new display so I can reset some of the settings to match my play (I like 5 ball rules).
Visitor Q, yeah, that's the game room in the background. I'm quickly running out of room and am now at the point where it's one in, one out. Now that Dragon's Lair is done, something's gotta go (likely Popeye).