Like the mystery of the split pin in the bottom of the bellhousing, here is another engineered leak point.

The rear wheel bearing hub has an oil thrower flange on the inboard end. The rear brake backing plate has an oil catcher flange at the inside diameter. The rear axle housing has a drain hole near the bottom of the outboard flange. Together these features provide a leak point for oil to escape in a controlled manner if the hub seal leaks. If it works as intended the leaking oil will drain down the inboard side of the brake backing plate rather than collecting inside the brake drum. For this to work the drain hole must be clear. This hole can be cleaned out using a 3/32-inch (2.5-mm) drill bit.