Like was mentioned .. They are sealed. If the bearings are bad, you will eventually have to replace it...
Those aluminum housings were not really designed to be serviceable, you can press the bearings out, but they are a pain.
If there is no indication that they have rusted, just run them a while and recheck them... :smile:KennyV
Two ball bearings on a shaft is never a good idea engineering wise unless meticukious care is taken to keep them in alignment.
Having both of them a light slip fit on the shaft is also bad.
Running them vertically is also bad
OTOH it is very cheap and will usually outlive expected service life