I have succesfully used a very high quality iso32 oil in toyota and nissan power pumps with added cooler installed infront of the trucks.
Smooth steering, and better heat tolerance.
Use at your own risk. Meaning dont blame here if you use "ghaaslate" power oil with no cooler.
If you can find mobil 220 atf. Its very close to the old dexron 2 formula required for power steering.
And change out all oil, its not just draining the little tank, the whole system is about 1.5 litres or so.