I re-cleaned it, then painted it, then put it back together...

I gave the motor a test without the blade, and everything seemed fine. So I started re-attaching the blade and realized there's another broken part. This thing that the blade attaches to is bent.

So we ordered that online, and also ordered the plastic housing that goes around the belt that drives the wheels in the front, since a metal pin in it had taken some damage and melted the plastic housing such that the pin was no longer oriented correctly, and we ordered a new discharge adapter since my mother lost hers. In all that cost $55. So I guess next week it will finally be able to mow grass again.

In case anyone is waiting in suspense, the parts arrived, I put the thing back together, and mowed with it for a few minutes. It seems fine. My mother tried it out too and she says it's faster now. (It's self-propelled.)