How often do you change your Hydraulic fluid and filter ?
Those hydraulic motors are used 24/7 on farm, construction, mining and military equipment for many, many years.
They are very efficient and trouble free as long as the hydraulic oil is free of moisture and dirt, residue.
Personally, I chang filter and fluid annually just like we do in our trucks and farm equipment.
If your seales are good and not leaking another 16 years is very do able.
For the miles you run.
Mine two are original, no leaks, 99 model with 130 thousand miles.
In my life time. I dont see changing mine.
Good luck.