Is the shaft of the motor horizontal? If so, the weight of the impeller is causing more wear to the lower part of the inner bushing and the upper part of the outer bushing, the one visible in the image. If this goes on long enough, the rotor can drag on the stator. If the electronics checks out, remove the blower assembly, take it apart and check for score marks on the rotor. If it's OK, the bushings should be good enough so clean the pieces, put a couple of drops of oil on the bushings, reassemble it and see what happens. Quite often, the oil goes away and what's left gets thick. Cleaning the old stuff away and relubing does wonders. Also, I see a bit of debris on the winding so I expect there's also some on the impeller too.
Best o' luck,