My brother sent me a link to this Site Years ago.
This has lots of Information/Opinions about oil.
You have to Weed thru it though.
Link:
https://bobistheoilguy.com/forums/
Also this link:
https://www.tractorbynet.com/forums/...shings.145754/
The 90 weight oil was safe for Bronze and (Yellow metals) years ago when these trucks was in there 20's.
This new oil.
Can you go Wrong with Syntetic or GL -12345?
If you keep these transmissions filled with some oil that,
Doesnt leak out faster that you fill it they will be okay.
