Phillips makes oils for older machines, they have a 10W Powerdrive Hydraulic Fluid for the vane type hydraulic pumps and a 50W Powerdrive Fluid/gear oil for the final drives. I use Kendall Super D 15W40 in the engines. I use Cat 30W Drive Train Oil in the transmissions. Find a oil distributor in your area, they can get you other brands also. Also depends on your climate, use the proper viscosity oils for your temps.
"i reject your reality and substitute my own" - adam savage. i suspect my final words maybe "well shit, that didnt work"
instead of perfection some times we just have to accept practicality
nearly all oil companies have a tech advisory service ring your chosen company and get a recommendation. virtually all engines where SAE 30 was recommended can use a 15w40 multi-grade diesel oil and for caltex that is delo gold multi 15w40 there is also a mono grade. multi grades have replaced mono grade in most applications as there is no need to change oil for winter operation and then change it again for summer use. unless of course you are in really cold areas in winter.
central alberta, -40 celsius isnt uncommon lol but likely i wont be needing to start it in those tmps and if it was an emerg i could hoard it in and use a herman nelson to warm it up.