My '99 S80 T6 has had random power steering boost since new. During warranty the dealer changed the power steering reservoir twice without improvement.
Out of warranty dealers have changed the power steering rack and the power steering pump, also without improvement. I just never know when I turn the wheel for a u-turn or parking maneuver if I'll have assist or not. Just another benefit of this quality product. The dealers can't fix it, and dread when you roll into their lot in a S80. As the technician remarked in disgust when informed by the service manager that he would get to work on my S80 as it was being unloaded from the flatbed truck (once again), "not another one of those POS". A tough but accurate assessment.