4 wheel drive not working on a low hour tractor...big deal? Rear drive will fail too?

Doesn't is seem unusual that the 4wd failed and it is now a 2 wheel drive at a few thousand hours on the tractor and tractor looks not old and is about 30 years old. Does this mean it was terribly abused, and might the rear wheels drive fail too? It has a front loader on it; do you think someone used that abusively to do this? It is a steyr 545 tractor, rare in US.