WCF,
A note on your very well done proceedure. You don't need to remove the "star" button to get to the wheel nut. If you run your fingers around the outside edge of the horn pad and lift up the entire rubber pad comes off. This makes it much easier to get to the nut and much, much easier when replacing it.

The first time I took out the cluster on my 1977 450 slc was because a small screw in the inside of the speedometer had come out jamming it. The screw is located inside the housing where the cable comes in. Inside this housing is the cup that rotates and drives the magnetic pick up that drives the speedometer neddle. As with replacing all the bulbs, it is worth checking this since you are already in there.

When you are inside the speedometer be VERY careful not to dislodge the little bar that runs across the top of the odometer numbers. It is swedged on one end but not the other. Mine slipped out and I spend an interesting but very tiresome 2 hrs. geting it back in. You need at least 4 and better 6 hands to get it back together.

Another thing I noticed about these speedos is that the little aluminum cone that is on the center of the needles comes off very easily. I had mine completely back together when I noticed that it had fallen off. A little dap of hot glue or something similar will hold it in place.