150,000 Miles OEM , 15 Year Old Transmission Fluid, Should I Change, Still Clear Red Color

[George_San_Jose1]

Fresh transmission fluid will have fresh seal conditioning chemicals. If only for that reason its a good idea to replace the fluid with a fresh batch. Auto Transmissions work under extremely high fluid pressures and therefore if the seals deteriorate enough to start leaking, the fluid pressure will drop, and all sorts of problems will eventually ensue. There’s no fundamental problem imo with using a fluid flushing machine to replace the fluid as long as it is done in conjunction with cleaning/inspecting the inside of the pan, and replacing the filter.