Ever since I started wrenching I’ve heard the whole “if the tranny fluid is toast you’re better off leaving it” thing plenty of times but how much truth is there to it? I see our master tech doing plenty of transmission work and he never seems too worried about the fluid it’s topped off with. My understanding of the idea is that if a vehicle has had the tranny flushes neglected past a certain point the added viscosity of the used fluid helps to prevent metal on metal but doesn’t more viscous fluid create more pressure that can interfere with the valve body? Also couldn’t the presence of any shavings or debris in the used fluid clog up the filter and cause more trouble shifting?