580B gear oil vs hytrans

If the manual states that 90 wt goes in transmission and tch goes in torque tube, why do the case dealers and parts store tell you that you can use hytrans for both instead of gear oil.

I never owned a backhoe before and I'm getting confused about all the different hyd fluids to use and where. like what hyd fluid do you use for the lift cylinders on the loader, what fluid for transmission, what fluid for torque tube.

Posting the same question in two different threads has the potential to cause confusion. I'll close this one, and any replies can be made here: https://www.heavyequipmentforums.com/threads/hytrans-fluid-and-regular-hyd-fluid.84221/