Transmission wear can be from oil contamination or the use of the wrong oil. In the first example we have the oil of a Toyota Land Crusier where the owner swore he never left the city or the pavement. We can see that the oil had 25% water, 1279 ppm of dirt, 75 ppm of sodium (salt) and more than 4200 ppm of iron wear and rust. The transmission had to be replaced and he wanted the dealer to do it under warrantee.
The operator should advise his superiors when he has to work in a river deep enough that it covers the axle. That way the oil can be changed without damage to the internal parts.