This is interesting, so I’m going to study it with a rusty shaft. The rust stream accumulates on the underside of the shaft and flows out from the right side of the nut.
This is the top side of the shaft. The bearing collar area is evenly rusted, but it’s not connected. 
Moisture has seeped in from the right side and the corrosion is very deep. 
The left side is shallower. To maintain the vehicle’s condition, I think it’s important to prevent rust from forming in the first place.
