Originally Posted by JARblue

I've done several PS fluid swaps for local Z owners with fluid between 60-120K miles old, and none of them were complaining about the steering.

My uneducated guess is that it's your steering rack. Take a look at the tensioner bolt on the steering rack under the car; don't adjust it - just look for a bunch of gunk around the bolt. I'm about to get mine replaced under warranty, but my symptoms are different. My steering got super loose all of a sudden. Tightening the tension bolt can fix the loose steering but it causes the gears to bind, which is obviously not a good thing over time. Over-tightening the tension bolt can cause the steering to stiffen such that it does not return to center during turns.