In my life as a mechanic. I have not seen a dirtier trans fluid. It was black, gritty, and particles of fiction pad. Forklift came in for transmission not going Forward or Back, Intermittently.

I have flush the system with Diesel Fuel about four-times (Filled, cleaned screen filter, run & drive forklift, drain system). After about 4-times, fluid looks about 80% better but there's still particles. I think the fiction pads are deteriorating, but why the black gritty particles don't stop?? The hours on the motor is under 3000-hours and the transmission does not slip. What do you think??