Federal Model 28 Possibly Warped?

[FromOuterPluto]

I picked up a Federal mod. 28 on marketplace yesterday, motor works good but was very stiff. Disassembled the entire thing completely, cleaned and re-packed bearings, freed a seized brush, etc. Got it all back together today and the impeller- when tightened down- has a slight wobble to it that causes it to scrape the intake shroud pretty bad. However, when the nut that holds the impeller on is backed off the impeller spins perfectly free on the shaft and doesn't strike anything.

Not sure what to narrow this down to.. Off balance motor? Bad bearings? Any help is appreciated- TIA.