That type of wear is most likely caused by an inner bearing getting a little rough and causing the race to spin on the spindle instead of remaining stationary and letting the bearing balls or rollers turn over it. In extreme situations where the bearing locks up, I've seen the underside of the spindle worn down 1/8" or more before everything pressure-welds itself together.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
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