Would it be a bad move to squirt a small shot of WD-40 or something CRC QD Electrical Cleaner into the hole where the cable goes in the back od the speedo?

It might be a blind hole, haven't checked yet, but I searched lubing speedo cables and a few threads mentioned lubing the head, or having a shop do it.

WD40 will lube it for a bit but will dry out. Use graphite powder, same as the lube for the cable if anything at all

Thanks Dale. I'll try some and see what happens.

I tried the graphite lube, and it helped. I put a couple of drops in the hole where the cable goes and also put a few drops on the gears that I could see. Then it was tested with a drill and the square drive portion of a broken cable. It still acts erratic, but at least it's registering now.

I'm not sure how they work, but it's acting like the needle doesn't want to go CCW when speed decreases, so I'm thinking that the problem, or part of the problem, is that something is gummed up or just too dry as far as the shaft that the needle's mounted on.

For example, if it's being driven and shows 40 mph and you downshift and brake to slow down the needle hangs around at 40 for a while.

There are a couple of holes in the back of the case for light bulb sockets, so I think I'll just try to flush it out with some quick dry electronic cleaner and relube with the graphite.

I'm really not too concerned about it because it's the wrong speedo for the car, but I'd like to get it working.