I punted and just got my hands on some older T40 and T42 keyboards. These have Trackpoint assemblies that use the older style 28-pin controller IC. I'll post some more details soon. The keyboards that I got were part of a lot that had been plundered for their key caps, but unfortunately a lot of them had the square post for the Trackpoint nub removed also, which is kind of puzzling. For anyone interested, the Trackpoint sensor is a set of resistive strain gauges printed directly onto a very thin PC board. There is a thin post that is epoxied to the center of a cross structure routed into the board. The black post that you see when you remove the red cap is actually another shim that fits around the thinner post that is epoxied on. If anyone knows of a source for this shim cap piece I'd love to know. (Longshot, I know). Anyway I've taken some pics, but I haven't had time to post them anywhere yet, but I will soon.
I know the shim cap you're talking about. I take my trackpoint cap off to clean it pretty often, figure mild cleansing a bit more often is the way to go. If you let finger gunk build up... Well, not only is it nasty, but suspect finger oil/acid speeds breakdown and "smoothing" of the textured surface. And the textured surface doesn't really lend itself to cleaning without damaging the texture. Man I hate seeing an old cap that looks like it's never been cleaned, especially if the owner wants me to use their keyboard for some reason, ewww!
Anyway, I remember my surprise first time the shim came off with it, thought I'd broken it, :laugh:. Don't know how likely it is you're going to find those shims as a separate part. Seems unlikely you could fabricate one either, at least I can't think of how. Maybe if you could find a bit of plastic or metal of the right size to fit a trackpoint cap, you could cut a bit off of the existing post and glue a bit of the right size back on, just thinking out loud, might work but sounds like a PITA. How many are you short?
Or, maybe, thinking a bit more creatively, the older style Dells caps
pictured here would fit without the shim? I don't have any to try, not even sure you can get them still, again just thinking out loud.