When the rubber on the thumb-stick wears down, just print a new one?

Clean off all the old rubbery plastic from the thumb-stick first as this is a snug fit so that it does not move around or fall off.  Put the cap on one side then ease the rest on with a small screwdriver or the like.  Be slow and patient and you should be rewarded.

I printed it with eSUN TPU95 oriented with the opening down with a PLA support structure using a 0.4 nozzle and 0.2 layer height.