See the little white tubes on the axle shaft, under the boots and bands ?
Those are the vent tubes, they allow the heat and pressure caused from the 3 bearings moving in/out and around to escape rather than build up, burn the grease, and cause the bearing to freeze or lock up Which can cause a host of problems including the the axle spine pulling out of the gear box.
Here's a close up of the venting. Those are bearings in the background.
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