821 power fluid is what AC calls their's.JD calls it Hyguard.C_IH has their own too but it's all the same more or less.Generically it's called hy-trans fluid.Made for modern tractors that use common oil for hydraulics and transmissions.Available at farm supply stores and most automotive supplies.Most farm co-op's sell oils and they would have their version of it as well.The containers should list on them what they are compatable with.The stuff I get at Rural King lists all the brands and trademark names of their respective oils(821,Hy-Guard,etc).Of course if you buy a new machine and put some other brand of oil in it and have a failure they are gonna say you had wrong oil.