Have you pulled the instrument cluster? If not, I'd say that should be the first step, so you can take the thing apart and see what is going on. Frequently the shafts and gears are making proper contact, but the little ratchet/dogs on the number wheels are worn enough that they don't make sufficient contact. Sometimes they can be fiddled with so they will make contact again, or the offending wheel can be replaced with one from a junked unit. Sometimes the drive worm gear is worn or has slipped out of position. If I remember correctly (it's been a while since I had one apart), there is a lock pin in there somewhere that can be reshaped, and that helps to make that gear make proper contact again. I've had some, at least tempory, success with that kind of repairs, but I must admit that they didn't last more than a couple of years and that, eventually, I replaced the whole cluster with a healthy one.
Bob S.