Ford Repair: Power Steering, ford f150 4x4, power steering fluid

Question
I have a 1994 Ford F150 4x4 with a 351 engine.  I am loosing the power assistance in my steering.  Sometimes it is there and other times it feels tight and I have to help when making turns to return the wheel to straight.  It also feels like it pulls to one side or the other at times.  I have had the geer box replaced thinking that was the problem and it seemed to help for a while.  All front end joints/components check out OK.  I looked at the power steering fluid and it looks almost milky to me.  Like wter got into the system and broke down the fluid.  Would this cause the problem?  If so how hard is it to flush the system and refill?

Answer
Hello and thanks for the question...I'll try to help.
 Yes, water in the system can cause steering failure/slipping. What I would do is disconnect the return line fron the pump and plug it. Then get a case of PS fluid, a bucket and additional rubber line. Then attatch the rubber line to the return hose and place the other end in the bucket. Start the vehicle and have a helper SLOWLY turn the wheel from lock to lock. Add to the system as needed.
 If this doesn't help/cure your problem, I would suggest replacing the PS pump.
Hope this helps,
Erik