Tony this time:
I've generally used PS fluid whenever it was feasible, however on a vehicle with a major leak this can get a bit pricey. When I was in college I had a '69 Barracuda with a major leak,being a poor student with a car that wasn't the easiest to get parts for it wasn't cost effective to put PS fluid in it. It was a 2 hour drive between shcool and home (came home most weekends) and if I filled it before I left it was empty by the halfway point. Eventually I simply stopped putting fluid in it, it had a huge steering wheel so you didn't really miss the assist. I drove it that way for a year and everyone said the pump would be ruined. Then the car went into storage for several years. When it came back out we re-filled it just for fun. Not only did the pump still work, but the leak was gone! System worked fine for several more years before the steering box started leaking again. The steering box has since been replaced but that old pump still works perfectly.
I'm sure that old system wasn't as picky as some of the newer ones and I'm not saying you should use tranny fluid but in a case where you're going through a tonne of the stuff it can be an alternative.