Axle bearings: how to tell if replacement needed

Basically you are looking for any side movement and when you rotate the bearing see if it rotates smoothly or if it feels like it has grit in it, or fetches when you spin it.

While you have them out and if they seem good, I would clean them and repack them. They do not get lubricated from the rear gear oil.

You will need a needle for a grease gun to get the grease in them.

They require a bit of pressure (race against the rollers) to take the slop out that you are seeing, it's called bearing preload.