Just replace the bearings! Or have the motor apart and see what the issue is!
Off my head, you'll need to
Tap off the fancase
Undo the bolt holding the fan on (cant remember if its a LH or RH thread though)
Remove nut and washer
remove first fan
remove the spacer egg timer shaped thing
remove the fixed fan
remove the second fan under that
remove the last washer and spacer bit if there is one
Then, you should see this
Remove the 2 screws and that metal bit should lift off.
If there are any more screws then remove those and the coil and armature should be removable
You might need to remove the carbon brushes, mark with a permanant marker which side goes where
You should then be able to have a look at the bearings. Depending on the size, I might have some, but it's been so long since I've had one apart I cant remember
Have a go, what have you got to loose!