Don't the ball bearings have an extended inner race that also serves as the contact point for the grease seal? If so, it definitely needs to move on and off of the spindle with the hub. To do that, it absolutely must be a slip fit on the spindle.
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
Love your enemies and drive 'em nuts!