I have systematically replaced power steering components on my 3.9L V6 after a burnt fluid smell resulting from running fluid level too low. I found that a groaning pump was a result of air entering the system . After inspecting the system, I noticed that the rack was was wet on the drivers side boot. Wasn't able to pinpoint where the fluid was coming from. Lines seemed to be fine. Another indication that something was wrong was a stiffness to the steering. I replaced the pump to find that I was still experiencing the same stiffness and over a few days hearing the groaning again indicating that I was still getting air in the system. Next replacement was the rack along with inner and outer tie rods. Lower ball joints were replaced about a year and a half ago. Still experiencing the same Stiffness in steering. I see that there is a power steering filter available for this car but can't find a location or any video or info on it. I sense that there is something that needs lubed that I'm missing somewhere. Any ideas? Hub bearings?