Lexus Repair: 1993 LS400 Power Steering Rack Noise, power steering rack, lexus dealer

Question
I have a 1993 LS400 with 140,000mi.  I have had problems with "grinding" noise from P/S when turning wheels especially when just starting up in cool weather.  

My Lexus dealer found no leaks in P/S system, but did add a small amount of fluid.  Recommends replacement of P/S rack ($1100.) which is what I already had the dealer do two years (20,000mi) ago. I have no desire of repairing the P/S system of this car every 2 years!  

Now for the good news - In the week since dealer checked it, I have not had the noise.  When I suggested to the dealer that perhaps the extra fluid resolved it, they said unlikely since they added such a small amount.  They suggested that perhaps this was a case of air being trapped in P/S system.  If so, is the air released simply by opening the P/S fluid reservoir or is there a more complex method?  Also, what is the likely duration before air is trapped in system again & the noise returns?

Thank you for your help!  

Answer
Hello, It sounds like the noise was from it being low. I would keep checking the fluid level to see what happens. Also It does not sound like a rack problem but maybe a vacuum switch that screws in to the side of the pump. If the switch starts to go bad it wil suck the fluid out of the pump and run it through your engine and burns it.