Tractor Repair: IH 806 Hydraulic fluid/steering., flow divider, point hitch

Question
My dad has a IH 806 Turbo Diesel, I am not certain of the year but could find out.  The hydraulic fluid gets milky from time to time and I understand this is common?  And related, the hydraulic steering did not work with full weight on the front but will when lifted.  All other hydraulics worked and fluid level okay but needs to be changed.  Can the lines freeze up to the steering to cause this if there is moisture in the fluid?  It also has started making a clicking/knocking noise in the hydraulic system around the seat/feet area and you can see and feel it in the control lines.  Thanks for any advice.

Answer
  Hydraulic oil does get milky when there is moisture in it and it does happen occasionally due to condensation and exposure to the weather.  The oil will not freeze solid when milky, but will become slushy and the ice crystals plug up filters and suction screens.  The steering lines will not freeze to cause the steering problem.  If the steering, brakes, and TA were all affected, then the pump would probably be worn out because they get their oil from the same pump.  If the other functions are OK and only the steering is weak, then the pump is OK and the problem is in the steering circuit only.  Possible causes are a bad steering relief valve, bad steering sump check valve, or a steering priority valve (otherwise known as a flow divider valve) that is stuck or has a plugged orifice, or an internal leak in the steering cylinder.  The 3 point hitch and remotes are not related because they get their oil from a separate pump.  It would be impossible for me to guess what the noise might be without hearing it.