I was just contacted by a fellow Zeiss Coudé telescope owner who informed me that the slots in the RA gear assembly are not for adjustment but in fact allow the gear to "float" on the shaft.
"I have just had a look at your cloudy nights thread and the new pictures
The dovetails you have circled in red are actually not for alignment but the opposite.
It is a very large shaft coupling that allows the gear to float on the polar axis, you should be able to slide the gear slightly about the polar axis.
This seems to me to be a clever solution to solve the problem in gear cutting that is the gear is never truly central so causes backlash at one side and binding at the other, very noticeable in most RA drives. One way around this is to spring load the worm but this has two major problems one being excessive wear to the gear and worm the second is wobble or jitter especially noticeable in windy conditions.
What Zeiss seem to have done is cut the gear and then remount the gear in the lathe by the outer of the teeth and recut the centre hole to match the gear.
The gear is then placed over the polar axis with play in it, the polar axis is machined truly central and the distance from the gear teeth to the central hole is now the same all around the gear. when you adjust the worm against the gear it slides the gear on the shaft coupling against the polar axis, the gap between the worm and the polar axis is now constant as the gear just moves to one side on the polar axis so the gear fills this gap.
What you end up with is no backlash and very little friction, so no wear and the motor can keep a more constant speed.
At first it seems complicated but is actually a very simple solution on a large scale.
If you cannot move your gear slightly I would say the grease has dried out and it would be worth striping, cleaning and regreasing at this stage, it is quite easy to do and also interesting."