You are right.it will be in your operators manual, or sometimes they are listed on the side panel. if not, call the dealer, they will ask what temperature range you are operating in and give you the spec. you can then cross reference it as cheap as you want to go. I try to get the best oil i can continually afford, its the cheapest insurance.
By the way, you should inform us of serial number of your machine or at least model of machine so that we can give you with operating manual.I have a Kobelco SK210LC excavator I’m asking for some input on which brand and type of hydraulic oil I should use in my excavator