Since I didn't want to risk having the same thing happen all over again, I let the stator sit indoors for about a week or so to dry out completely.

Meanwhile, I fitted the bearing that was loose by first freezing it for an hour to make it shrink in size, after which it just slid right in place.

When I figured the stator was entirely dry, I put the motor back together. I made sure there were no irregularities causing gaps between the main piece of aluminium and the cover plate which could cause water to leak in, and screwed it back together.

I took a video of it running again on the bench, but it somehow disappeared and now I've put the scooter back together. I can tell you though, it feels like brand new again! The bad sounds and vibrations that I had gotten used to are completely gone, and I can ride nearly double the distance before needing to charge. So all in all I'm very happy with the result!