I would recommend a Fluid exhange, not a flush, You use the vehicles tranny pump to change the fluid versus the machine and not kick up debris, I just had this done on my Ford F150 and seems much safer than the forced flush with additives and cleaners. I suspect that some of the cleaners can be a real disaster on a old tranny. The way it works is the line is disconnected from the tranny to the cooler and the machine is put in series, than the car is ran in park which allows the Transmission pump to push the fluid through the cooler and transmission. No additives, no cleaners, no forced pressures.