These motors normally use a sintered-bronze, graphite embedded bearing. They are normally pretty reliable but they can get clogged with a combination of graphite and contaminants from the air. I would first try getting some WD-40 or other penetrating lubricant on the motor shafts if you can see them. It would work best if the fan was running if you can safely get some spray onto the shafts' ends. BTW, WD-40 is not a lubricant and evaporates fairly quickly so isn't good for sewing machines for example. A resin-free light oil such as 3-in-1 is much better; it doesn't evaporate fast or leave sticky residue when it gets old.
Answers & Comments
These motors normally use a sintered-bronze, graphite embedded bearing. They are normally pretty reliable but they can get clogged with a combination of graphite and contaminants from the air.
I would first try getting some WD-40 or other penetrating lubricant on the motor shafts if you can see them. It would work best if the fan was running if you can safely get some spray onto the shafts' ends.
BTW, WD-40 is not a lubricant and evaporates fairly quickly so isn't good for sewing machines for example. A resin-free light oil such as 3-in-1 is much better; it doesn't evaporate fast or leave sticky residue when it gets old.