I vehemently disagree with this statement.
All fluids degrade from heat, collect condensation, and lose additives. The same principles are applied in our tractors with wet brakes, power shift or power reverse.
All the equipment I’ve worked on specifies a drain interval for the transmission and/or hydraulic system.
I’ve never had a transmission perform worse after a service.
If the new fluid causes a substantial loss of performance, that means that particles in the fluid, or degraded viscosity, was compensating for worn clutches or a dying pump. You did not cause a problem, you exposed an underlying issue that was simply going to continue to get worse.
In my mind a good analogy would be “never change the oil in an old engine because it will leak.”
That may be true, but how much damage is being done by that gummy sludgy oil?
I’ve had many poor performing hydrostatics come back after flushing the sump and refilling fluid.
GM electronic transmissions in particular are sensitive to fluid quality.
