[sparkycuda]

Grey/milky hydraulic fluid often means water is getting in somewhere. Could be high humidity getting in through tank vent or filler cap (does it have an o-ring that is defective?), etc. I presume your have emptied the hyd tank and flushed all lines and cylinders? What are the operating conditions? Outside, in water or rain, model stored in high humidity area? What about your new hydraulic oil? From a previously opened container? Does it look grey or milky sitting on the shelf? (Don't shake or agitate before opening bottle - take a look inside. Could be contaminated.)
When did this start? Have you changed brand of hydraulic oil? Sometimes different brands or types can interact with each other.

Good luck!

Ken