I had a problem with differential oil leakage from the rear wheel bearings, and after putting in modern seals, etc, etc, learned from our local Guru, Fred Houston, that the proper diffie oil level is well below the filler plug: "just enough to barely be able to reach it with your pinkie finger".



As as the diffie oil lubes only the diffie and the inner axle bearings, only enough oil to reach the ring gear is needed; the ring gear will throw it around enough to lube OK, similar to the flywheel lubing the tranny.



It's easy to forget that the outer bearings on T's are lubed by the two grease cups at the ends of the axle housing, and if enough oil is in the axle housing to reach them, they'll leak.



Back in the T era, there were many fixes sold for rear axle leaks; imagine this was because folks were overfilling then, too.