I had a similar problem.I wanted to change the hydraulic oil on my O Turn Toro. The operator's manual said the hydraulic oil is good for the life of the machine. I located the spot where the fill plug is, and bored a hole in the floor of the machine to get at the plug on each hydraulic unit. I was able to draw [suck] out about 3/4 of the oil. To replace the oil I went to the local autoparts store and the guy [ who I know} said that the Skag guys use 15-50 synthetic oil for the hydraulics. So I did also and the machine works fine, and yeah the old oil [16 yrs] was dark, and dirty.