2011 Impala power steering issue

I have run across a dilemma and I haven't found a solution. Vehicle is a 2011 Impala LT 3.5l with about 190,000 miles.

Started having power steering issues, lack of assist plus pump whine. A leak developed which became bigger. Added dye and located a leak on the 5" rubber hose section of the fluid return line/cooler line. Replaced the line and added new clamps. Filled and bled system. Started car and still have a whine. Fluid had bubbles despite what should have been a good bleed.

Replaced the power steering pump thinking it had gotten damaged from low fluid and this was causing cavitation. Went through bleed and fill again. No bubbles when turning side to side with vehicle in air and not running. During the bleed process I did not see any of the dye come into the reservoir.

Started the vehicle and let run for a short period of time with turning side to side. Still a lot of pump whine. No obvious bubbles in the reservoir when it is running. As soon as the vehicle is turned off fluid backs up into the reservoir and the fluid is filled with bubbles.

Seems to me that there must be a backup. Is there a way to determine one of the hose lines versus the rack itself?

As an added note the rack was replaced about 2 years ago, roughly 50,000 miles.

Any help or insight would be appreciated. Thanks

The leak detector agent may have some form of surfactant as part of its ingredients. It might be time to completely drain the system and refill with fresh hydraulic oil.