I use Mobil 1 Synthetic ATF in my P/S systems along with a Magnefine filter. I change the fluid using a turkey baster in the reservoir (which removes maybe 40% of the fluid at a time) perhaps once every two years.
One P/S hose failed because the metal strap securing a motor mount had broken and bent back to chafe the hose at the metal fitting. Cutting away the strap and replacing the hose fixed the leak.
The other rack is just leaking all over (both ends and the end of the steering shaft). I can't explain it since the pump is fine, the fluid is clear and the filter is relatively new. Jorgens replaced it on warranty. I will flush the fluid as they require when a new rack goes in.