Sell them to get a new one, for a new bike, or if you want one in a different colour? I'd say Kings are virtually flawless too, much like any hub, they need looking after, and many people would say a service every 6 month is a good way of keeping them running them smooth, but as is the case with any other precision part, if you don't look after them they will die, so it's not really too much to ask to check it over once every 6 months..