Just started getting ps whine noises from the pump of my 09 legacy (non-gt)... Was ready to pull the trigger on picking up a new pump, but will DEFINITELY try replacing the o-ring first! No signs of leaking from the rack or lines, but definitely signs of fluid leaking on the top of the pump housing... seems like a really slow leak though. I cleaned it up so I can find the source, and fingers crossed, its because of a $2 part.
Thanks for the insight!