Can someone please tell me what 600 W steam cylinder oil is? A definition of suitable oil for 1928 Durant gear box, clutch throwout and rear differential would be very helpful. Someone in my locality has suggested SAE 70-90, API GL5.
As I recall, 600W was sperm whale oil which became illegal in mid 1970's..
In my past life, we used Steam Turbine oil in gearboxes. For anything with brass
or bronze parts in it, lubricants of the GL-1 type are often used. Sometimes sold
as worm gear lubricant. This becomes a factor if the loads cause heat in the brass.
Just idling along might not matter. There might be a black market for your 600 drain oil.
For a century it was used for everything from sewing machines to automatic transmissions.
Now Jojoba oil replaces it, but costs a lot, like $25 per quart..