non-hypoid trans oil for a PV 544?

[Bob McCombs]

Baffling... In my final prep to get a 544 on the road, I found so little oil in the M4 trans that I drained it. Amber and clear with an odd smell. Huh. Checked an origional '59 owners manual (mine's a '60). In both the "General Lubrication Instructions" and the "Lubrication Diagram" it states "DO NOT USE HYPOID OIL". I've been in the auto biz in both parts and spinning-wrenches for 35 years. I've sought opinions high and low and they rang from "B.S." to "Hmmmm..." Our local petro distributor says he's had this question before and sells an air compressor oil of doubtful viscosity (AirComp Indy 30 [not an SAE rating]) in 5 gallon buckets.
Someone must have bumped into this before. Help! Tomorrow I purchase 5 gallons of a mystery substance and install it... Thanks

[Bob McCombs]

Mystery solved. "lubetek" at Chevron did some research and found that Volvo calls for a GL-1
MOTOR oil, 20w in the M4 tranny of that year. Being Chevron, he recommended Delo 400 20w, which is a highly detergent Diesel oil...