you could have chipped one of the magnets inside the housing.
they cost about 60 bucks
take off the prop, undo the two screws on the back plate, pull the winding / armatures out there is some resistence from the magnets. see if any metal / magnet chips come out. if your careful you might be able to re-use your seals, but if you think the screw threds damaged the rubber put in a new gasket pack. about 25 bucks.
if magnet chips come out, clean them out thoroughly, you can put it back together and run it with cracked magnets, there will be some loss of power, order a new housing with magnets and then disassemble and reassemble when the housing arrives, this time get a gasket pack and new armatures.