I just talked to the local Hobart service company in Spokane, WA, and he told me that any 40 weight, non-detergent oil will work. He also suggested it is far cheaper to just get it at a local auto parts store, since we are over 120 miles away from him.
Nice guys… I like their honesty and not trying to extort some kind of expensive consumable for their equipment.
Oh and just to be clear, this is the gear oil added in through the top of the unit. I think it is a different for the planetary… some sort of food grade like George mentioned.