On my last few drives I noticed at highway speeds the car is wandering a bit, steering doesn't seem to be centering well. For instance if I merge left the steering seems to hang in that direction a bit and I have to center it. My suspicion is the steering rack, with 150K miles it's probably due for a rebuild, but I'm hesitant because it's not leaking any fluid and the PS pump sounds fine.

From my understanding the only thing done in a rack rebuild is basically replacement of seals, so if mine's not leaking I'm not sure a reseal will fix anything?

 

Is your power steering fluid reservoir full? Have you jacked the car up to check for any looseness in the tie rods and ball joints?

 

PS fluid was just above the min line, always has been, but I topped it up and no difference. Ball joints and tie rods are relatively new, done at 135K, so don't think it's that. I can even feel it a bit in tight corners, the wheel just doesn't seem to want to come back like it should.

Maybe there are internal seals that keep fluid in certain areas and those have failed?

 

an alignment? I just did mine using the string method and it is night and day. It doesn't ake much change to make a dramatic different in how your car holds a line. Too much or too little toe-in makes a world of difference. Generally speaking, if your car wanders after an alignment, then you would strongly suspect worn suspension pieces. But you had already said that those were replaced in the last 15K miles?

 

Have you checked the rack end boots for cracks? My steering was sluggish, because over time dirt had gotten in a slice in the boot. Had to replace rack.

 

Assuming you don't have wear issues your problem could easily be caused by lack of adequate
caster. It's caster that creates the force to straighten the wheel.