i found myself in the same situation
i just bought my car with a broken rack
i replaced the rack
then i realized that the car's power steering pump is dying because i would have to rev up to get power to the steering
so i replaced the pump with a used one which then blew the power steering high pressure line
i got my line repaired by a hydralics place
they reused the fittings and the restrictor thats in the line
after i installed the line, i would never be able to bleed the system
i would bleed it til there were no bubbles, but as soon as the engine was started, foam would start to build up in the reservoir
i thought it was the pump again so i replaced it with a rebuilt one
same foaming problem
so i thought it was the reservoir being clogged up, so i gutted the reservoir.
same thing
before the line went, there was never a foaming problem
we inspected the line and realised that it was a little to short and thinner than the original
i will be bringing it back to have them redo the line
i believe that the line has too much restriction causing the atf to be over heated in the pump causing the foam
hope i am right