Retired gentleman
Thanks for the advice. I actually found an earlier thread where you had suggested peening the tangs to get a tight fit in the slotted disc. I did this, and it helped a bit, but it appears that the problem is that the spine of the weight is actually worn from slapping into the stop.
The advance springs that were on the bike when I got it were loose, so I ordered replacements from mike's which needed some shortening to get the proper return. Not sure if the looser than normal springs were the cause, but there is a visible wear mark on the back of the weight where it contacts the base.
I would love to find a replacement set of weights, but it appears that the easiest fix is just to replace the advance unit.
I ended up fitting a piece of shrink tubing over the worn area of the weight and it now shows the timing to be correct at both advanced and retarded positions. The tubing works, it just isn't much of a permanent fix. I feel a need to check it every couple of days to make sure it hasn't come off.
Again, thanks for the advice. I'm sure that this works in many cases. Mine were certainly loose in the slots, it just didn't fix my particular problem.