I never understood that design although I am being told it was not unusual at the time.
If one wanted to have the wheel bearings oil lubricated (as they are in a modern truck) the whole "diff gear oil runs outboard through the axle housing and lubricates bearings" stuff makes sense.
If one wished to have the wheel bearings greased, why not choose a design similar to the front axle where there is seals inside the axle tube to actively prevent gear oil from flowing to the outboard side and avoid oil contamination of the greased bearings?
Instead we have a design that allows the oil to flow all the way to the hub, being held back only with iffy components (cork wedge/gasket) that may last for a long time, or not at all (if not put together exactly right), or fail randomly at any time interval, resulting in contaminated oily-greasy bearings and leakage of gear oil into the brake drums and to the outside.
I thought that, maybe, this design is intentional. A fail-safe; have oil lubricate the bearings is better than no lubrication - but it was explained to me that this is not a deliberate or desirable outcome.
As I said - I never understood the reasoning for THAT particular setup.
Way back when I bought my truck it had six leaking axle seals. My joke was, I can fix this by parking with a strong sideways tilt; that way, only three seals leak, an instant 50% improvement.
