Transmissions and pwer steering systems are pretty much closed systems. They do not get the daily blowby of combustion gases, dust and dirt, atmospheric moisture, etc. So the ARX stand is that the product is best utilized in a cleaning mode prior to fluid exchanges in these sealed units. A better question is how long does one run the ATF or power steering fluid. Read an owners manual and it may state that the ATF is good for 100,000 miles. Ask a transmission rebuilder and they would likely say 30,000 miles or every two years. You will likely find the same paradox with the power steering. I would tend to believe the optimum change out time is somewhere in the middle for average driving or use. The main thing hear is to utilize ARX to dissolve any oxidized lubricant back into suspension before the fluid exchange. Hense get a much better drain, not leaving gummy residues behind, especially in torque convertors. Why put fresh fluid into a dirty system?