It looks to me like the bearings were permanently lubricated. My fan is also often noisy and the rotor doesn't turn easily by hand. Sometimes it has stopped running. I cleaned the bearings superficially and lubed them with a little heavy oil. Also I cleaned up all connections and the commutator with very fine abrasive. This worked for well over a year but seems to be going bad again. I guess water and dirt get in sometimes.

Did you somehow get the motor bearings out and relubricate them? Do you know if they're available by themselves as a replacement item?

Many thanks.