Can you feel the end-play or see it ?? would the rear wheels feel sloppy or how would I know if it needs adjustment.??
A gap may be visible as Brian said. ....I have seen transaxles that were so loose that the tractor could be pushed with the wheel-lock pin engaged. ...Other times a tractor might drive OK on flat ground, but would not climb a slope or move under load.
If axle end-play is neglected too long, some expensive parts can be damaged!