The sealed two sides cartridge bearings are easily serviced in place and should be.
Flip out the seal on the exposed side with a knife point, save it carefully.
Wipe out the old grease left on the balls with toilet paper.
Wipe, wipe,round and round untill mostly clean.
Use no solvent!!!
Wipe in new grease(I like disc brake wheel bearing grease in a red tube at Ace hardware)
Pop the seal back in/on.
Done.
Bill