In addition to replacing the PS fluid w/syn, I also splice in a Magnefine filter on the return line. Pretty much a lifetime filter for auto PS systems. Catches any wear metals befrore they can do damage.
I used Mobil1 Synthetic Dexron III in my dad's Lexus ES300, using the turkey baster method, and the results were EXCELLENT. The steering felt smoother and easier than when the car was new.
Mobil Synthetic Dexron III has been relabeled Mobil Synthetic Mercon V, and says on the back label it also works in Dexron III systems.
My dad no longer has that car, so I'm looking for someone with another Toyota product, so I can use Dexron VI in the power steering.