Bearing staining is the first stage indicator of an overheated bearing. It doesn't just happen for no reason. This is not my personal opinion, this fact comes directly from the experts at the bearing manufacturing companies. All good bearing manufacturers publish this fact in their failure analysis documents. They will also highly recommend investigating the issue and not just putting the bearing back into service. You can wash it off and re-use it, but you're just putting a bearing that has been taken to the edge of permanent failure back into service without figuring out why it almost failed.