I spray starting fluid (aka ether) into a shot glass, drop in the bearings swish them around a bit and let them sit an hour or so. Cover the glass or the ether will evaporate. It's about the most volatile solvent you can get. Take them out, put them on the end of a pencil and spin them. If they're smooth and fast, they're clean. If not, it's back into the glass. Most shielded reel bearings can be brought back to life this way. When clean, lay them on a paper towel to dry. When dry, they will not spin so fast or smoothly as when they had ether in them to lubricate the balls. A drop of fine oil will relube the bearing. Bearings usually run smoother in one direction, that is the direction they were broken in, so put them back in to rotate in the same direction.