I use the universal ( hi priced ) hydrolic oil that says cat approved on the bucket for the transmissions, brakes, and hydrolics
It has come down some but is about $29.00 per 5 gallon bucket.
At TSC it comes in either 10 W or 30 W - - - if you use the 30 W it is a little cheaper but you might end up with hard starting in the cold months! I got some of the 30 W by mistake once and put it in the 310 JD backhoe hydrolics one winter and it was hard to start and hydrolics worked hard for about the first 5 minutes after an over night set. I called the dealer and was told it would not hurt the machine but I pulled it out to keep from burning up a starter.
My 980 Cat manuals call for 30 W above 70F and 10 W below 30 F but I just keep 10 W in year around as the dealer In Indianapolis recommends it unless you get enough hours on a machine to require changes more than once a year.
In keeping that on hand I use it in the John Deere equipment, Komatsu, Cat and BobCat. My old 840 Allis Chalmers loader I use Dextron in the transmission as it is a 1972 model and that is what the manual calls for.