It seems the bearings in our cheap blender last about a year, even if we don’t put the impeller in the dishwasher.
The top bearing, the one nearest the impeller (on the left in the pic), developed detents, which says at least one of the balls has failed.
Both bearing housings are rusty; water has no trouble getting past the flexible seals at each end. As they’re not immersion-proof, I assume the water has little trouble getting past the shield rings on either side of the balls.
I replaced both of them, squeezed some silicone stopcock grease above the top bearing in the vain hope of excluding liquids, and we’ll see what transpires.