Gear lube for '46 Ford rear end

The owner's manual for my newly purchased '46 Ford recommends 140 wt. lube for the rear end. A local shop that specializes in antiques and cl***ics swears by 600 wt (yes, that's right) lube. They showed me a plastic quart bottle and told me it prevented leaks. What's the experience of the HAMBers?

Thanks for any suggestions/opinions.

 

NO 600! That is an ancient formulation from before the early thirties, when ancestral forms of the modern 90 and 140 types were made specially for spiral contact gears. Use 90 or 140 modern stuff. Banjo needs only functional end seals and original (not tapped) threads at axle housings to keep the goo on the inside.
Ford went to early forms of the modern lube in 1932, and changed the specs to ep 90 and 140 for these earlier vehicles as newer formulations became available.

 

Thanks Bruce. I was imagining using my wife's hair dryer to make it viscous enough to fill or drain the 600 wt.

 

The Model A people continually discuss 600W, and have sources for the real thing, still available for some purpose, and also discuss a bunch of whacko subs***utes like STP... I don't know wheteher Ford EVER actually specified it. I believe the Model A car manuals and also the Service Bulletins just specify something like "good quality gear lubricant".
The Model A rear gears were used in most '32 Fords, and by then Ford specified an early form of modern formulations, something like 220. This rapidly changed to the familiar 90 and 140 over the next few years, and 90 or 140 are specified for all early Fords retroactively. Model A trans might still need the 600, as there is little more than blind faith to keep the goo inside on those. Remember that 600W is not 600 weight...the designation is the manufacturer's designation...but it is a lot heavier than modern gear lubes made for spiral or hypoid gears. It has no place in any V8 Ford application.

 

Truck open one should have real seals at bothe ends and run pretty dry. Where did it leak, at the cluster shaft?