Update. I should have replaced the other bearing at the time, it also seized 3 months later.
The dry and dirty brush roller axle caused the plastic surround of the bushing on the axle to become hot and malleable. When the plastic cooled after use, the axle was now off centre as a result of the belt pulling the roller over to one side in its stationary position.

This is the process I used to disassemble, diagnose and repair the bearing, saving me from having to buy a new brush roller.
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