asking more Questions - hydraulic oil

[Pyrochase]

So I bought a 555-a and I need to top off some hydraulic oil and I need to change some if not all. What hydraulic oil are you all using / Should I use? For more information the lift system oil is milky so I know I will need to drain it and flush it with new fluid and probably to it again. If I am flushing the system can I use cheaper oil?

Thanks
Chase

[Lavoy]

Reasonably sure that is actually HyGard or equivalent, not common hyd fluid. If it is, anything meeting J20C Deere spec will be fine.
Lavoy