How can you tell if gearbox is going?

[chalky123]

As in the title really, how would you know if it was on it's way out, and what would you do to test it? 5 speed open diff. Thanks

[ThatPhilBrettGuy]

Generally without taking it apart you can't. I've seen some that make odd noises run for 10k miles+ with no issues. Most show no signs then one day its a bag of spanners or just no drive.