not sure if you followed the recommendations contained in my post on your prior thread regarding this matter -- namely:
this might help -- written for a 993, but seems to also apply to a 964
https://www.pelicanparts.com/techarticles/Porsche-993/36-STEERING-Power_Steering_Fluid_Flush_and_Bleed/36-STEERING-Power_Steering_Fluid_Flush_and_Bleed.htm
Specifically "To bleed the system: Refill the reservoir and quickly turn the motor on and off; this will cause the level in the reservoir to drop rapidly so do not let the engine run long as this can introduce air into the system. If possible have a friend watch but do NOT let the reservoir run dry. Once you can start the engine and the level does not drop let the motor idle and turn the steering wheel quickly and at an even pace from lock to lock several times to bleed the air out of the system. Do not force the wheel when turning. Continue this procedure until the level remains constant and there are no more air bubbles in the system. "