[rotorwrench]

The old 600 steam cylinder oil is largely outdated by more than a few later developements in gear lubricants over the last 90 years. The 600 oil was not graded by the SAE. A more modern lube would be an SAE 140 type gear lube so it's not all that easy to find either. Now days the SAE 85W/140 GL5 is pretty common and can be used without worry in a rear axle. The High EP could be harsh to soft metals in a transmission but then a transmission would likely work better with a less viscous grade like SAE 80W/90 which can still be purchased in GL4 medium EP. The model A transmission doesn't have as much soft bushing or thrust bearing material in it but it does have some.