The main difference is quality muffin fans have ball bearings, while almost all the shaded pole ones have sleeve bearings, which don't last as long. (ball bearings have better seals and lower wear even when the seals are shot.)
But those are huge. The ones I was posting would give you a 130 mm wide blast of so much air they'll lift themselves off the table: a laser blast. Yours are probably more like 400mm in diameter. So, yeah, replacement of the motor is probably a better idea. Then it's a matter of trying to figure out how to bodge together a connection between the motor case and the bracket that attaches to the whole contraption. (Presuming the shaft size is the same. If you have a smaller shaft on your replacement motor I can cut a bushing that'll take up the difference, very easily.)