I'm late in on this one, The dealer "special fluid" has a Mobilfluid424 spec on it. You can research that and find some fluids that cross over including Amsoil's ATH
hydraulic fluid. I run it in my 247 QDII & sell lots of it to jeepers for that application.
Also on the gear oil issue I have a White Paper showing some test results of different fluid brands that some of you may find a good read. LINK HERE
. It gives the ASTM test procedure and the result on 14 gear oils.