A PS problem just surfaced during my trip from Johnson City, TN to Cleveland, OH. The PS pump started to whine. I found the fluid in the resevoir was low so I filled it. Whine went away but now when I turn the wheels left or right I meet intermittent and inconsistant resistance. If i turn into a right hander it fells like the steering is power assisted then it's not then it is. Could the solution be as simple as replacing the fluid and possibly using a conditioner to unstick a pressure relief valve? or do I have to replace the pump & fluid? If so how do I flush the old fluide from the system?

See where it's leaking.  Often under the reservoir on the PS pump - look at engine underneath it.

 

I've had excellent luch with Lucas Power Steering goo for most of your problems except stopping the leaking Oring under the reservoir.

If I need to replace the high pressure hose and resevoir O ring how do I purge the system of old fluid?

Just had same problem .I found the hose was leaking at clamp where it whent into pump never would know it was leaking looked good but was sucking air steering same as you described did not have to bleed or anything  new hose and clamp filled resevoir problem was instantly gone