Bearings can be cleaned by removing the seals (there is usually a very small clip of some kind running around the outside of it). Then you could use an RPM Bearing Blaster and spray motor cleaner/contact cleaner through it and re-oil. You could also put them in a tea infuser and swish them around in Naphtha and re-oil. Or just by new bearings from Avid RC for $1 each and not spend the time on cleaning them.