Rear axles rarely give trouble if they have oil in them and not water.
Bearings and seals are generally available and easy to find.
Entire rear axles for these trucks are essentially free, if you need one and ask around they turn up, and aren't desirable for any other application.
More modern choices also exist, but to keep your same bolt pattern the newer versions have rear disc brakes, which then would require adapting front disc brakes to complement them, also possible.
Otherwise many other newer axles can be made to fit, some better than most, but wouldn't have same bolt pattern.
If you like these trucks there's no reason not to have one, they are all quite serviceable and easy enough to get about anything you could ever need. Also quite adaptable if you want more modern stuff and not all original, while maintaining original appearance.
