Working on details after work this week, I finally found an o-ring to replace the loose one on my speedo drive gear. The one that was in there seemed loose, definitely worn. A new one of the same size was nearly as loose. I tried a thicker one, but it was too thick and wouldn't allow the gear to slip in without excessive effort which also damaged the o-ring. Finally today I found the correct size. This is one of those cases where you must use a metric o-ring; SAE sizes are too thin or too thick. With the correct o-ring on the gear drive it popped right in with the correct amount of pressure.
Here you can see the gear, and a selection of o-rings. From left to right they are the too-thin one, the correct metric one and the too-fat one. The old one is below.
The packaging on the correct o-ring:
Here you can see the gear, and a selection of o-rings. From left to right they are the too-thin one, the correct metric one and the too-fat one. The old one is below.
The packaging on the correct o-ring:
