they seem to always Rust out. ive never changed a bearing but i did remove it from the bar and soaked it a kero bath. then spun it up on a drill to free up a bit of that rust. to finish i packed it with a thin grease. it will never be as good as new but will last a bit longer
Go to a skateboard shop they'll sell you one for a couple of dollars or maybe have a spare one for free then pack in grease Vaseline. has worked fine for me for a couple of years now.