How old is too old?

[4x4moses]

I have reached the 400 hr mark on my Kioti DK4510. The owner's manual says replace the hydraulic oil & filter at 350 hrs; but I have procrastinated. The owner's manual says a complete fluid change requires eleven gallons. I have two 1-gallon jugs of NAPA premium fluid, and about half a 5-gallon bucket of same. It's new fluid, but it's been sitting here for about FOUR YEARS! Knowing that hydraulic fluid is hydroscopic (attracts water), is this old fluid safe to use? Or should I just discard it and buy all new fluid?
I ain't the smartest guy around, and I'm only mildly mechanically inclined; so I'm hoping to tap the vast reservoir of knowledge available on TBN!

 

[oldnslo]

Have the containers been opened or are they still factory sealed? Where they stored in a climate controlled environment or in an ambient temperature building with temp and humidity swings?

Myself I would consider the above and fluid costs vs potential for major component failure if fluid is contaminated.

Other option is pull oil sample from your tractor and get it analyzed to see if fluid does need to be replaced.