check the bearing on either end of the armature shaft.....check for any end play and lateral play. Separate the motor out,  put electricity to it (don't shock yourself!) and watch the armature....I think you'll see your answer. Bearing will do what you describe when they run dry/dirty as well.

Kevin

there has to be a sintered bushing on the other end...something.

Kevin

a sintered bushing. Some are dry lubricated some are wet. 3 in One oil is not the best, but they do make an 20wt oil in the little squirt cans specifically for small electric motors. Comes in a distinctive blue & white can so as not to confuse with 3 in One. Mars Turbine Oil is better yet. Dry lube sintered bearings need to be replaced with same, as it's nearly impossible to imitate the dry, impregnated process they use.

Kevin