End play on the armature is not too much of an issue since it drives a spur gear. You do not want so much end play that the commutator will hit the brush holders. This problem is not easy to correct as the pinion is pressed on the armature shaft.
On the worm shaft end play, this is controlled by steel balls in each bearing block. I have never seen them missing or with wear on them, but you might check. I think the important thing is that end play does not allow the worm wheels on the axles to get in to an area on the worm shaft where the worm is not fully cut.
On the brushes, I am not home now so I can not look up the proper brush length. Hopefully someone else will post this data. They are the 2020 brushes, which are quite long.
For this problem also look at the side play in the driving axles. Since these wheel sets go in from the bottom and do not require pulling wheels, they are easy to check. Frequently when the current collector is removed, which is what retains the driving axles, the four ceramic insulators are broken. I would suggest you have a replacement set prior to taking this apart.