The fleet I work on rarely gets a fluid flush. Modern vehicles, lifetime expectancy of 10-20 years or close to 200,000 miles. But, these vehicles are inspected regularly and thoroughly. Every 90 days, for some. A flush will occur when the vehicle requires it. But for the life of most of them, it just won't happen. The system stays sealed.
A different story when it comes to the '46 International or '65 Ranchero that are also part of my fleet. In fact, out of the three axles on the '46, I still need to stainless sleeve the slaves on one of them so they last longer than usual. Wheel cylinder leakage used to be a regular occurrence with that truck.
I guess my point is, know your vehicle and maintain it accordingly.
BTW, DOT 3 on 95% of my fleet. Forklifts and EV's think they are more special than the rest of the vehicles.
