HP-67 with some odd good and bad things

[[kby]]

I recently picked up a '67 fairly inexpensively as it was sold as for parts/not working, the user stating he just got a flickering display. I originally got it as I have another mostly rebuilt -67 that is missing a few keys (they should be around somewhere—lost them when the -67 had some other parts used to fix my true love, which is a -65).
Anyway, I pop the battery in and the calculator acts fine upon turning on. Trying to read a card started the motor but didn't pull the card; figured it was just the usual gummy wheel issue. So I took the back off. There was some white residue mostly in the battery compartment. I presumed it was KOH from a bad battery, but it won't all go away with vinegar, so I'm not sure. Isopropanol actually removes black from the plastic, but when it dries it looks greyish. There was also some tell-tale green (copper) corrosion on some of the connectors, and a significant amount of rust, which looked to be mostly from the screws (the part of the label that covers the screw holes had two solid brown powder prints stuck to the adhesive; there was also a light rust stain on he keyboard. That mostly cleaned up except the plastic.

Now is where it gets to the first interesting part. Upon taking apart the card reader. the wheel wasn’t suffering from the usual gummy wheel problem. And unlike other wheels I've seen it wasn't white or natural latex yellow, but basically black. It had some of the white dust which wiped off, and I treated it with some rubber renue, although not much black came off. The wheel is soft and pliable and (decided to transplant to a -65) works just like new.

I am fairly sure from other signs that this calculator has never been opened up—label was basically pristine, plus, as I mentioned, the rust prints on the underside of the label. Has anyone seen anything like a wheel not made from the polyurethane?

This calculator was made in Singapore and the SN molded into the case is 1808S02243, matching the Singapore label.

Although I have successfully used both the square and regular o-rings, they don't seem to work as well as the original for me; usually the start slipping on the inside unless glued (cyanoacrylate) and they don't stack quite long enough (so if not glued one tends to wander away from the other). I have tried the silicone tubing but the stuff I get ends up being a little too small, stretches, and is hard to cut exactly (too long and it binds; too short and similar issue as with the o-rings, and it seems to be soft and degrade on the surface fairly quicly.

Now for the problem part. I was in the process of adjusting the card reader, and at the beginning of this, it appeared everything was OK with memory and stuff; just not reliable with the cards. Somewhere along the way I found that it couldn't be programmed in the sense that key presses would advance the step number, but all registered as R/S (the default fill). The same keys would work fine in run mode. I thought I saw someone here ask about bad RAM (or I guess RAM/ROM) chips in a -67, but I couldn't find it so if anyone can point me to that I'd be grateful. The issue is on the CPU board; switching to a dfifferent (good) CPU board fixes the problem.