tonight my ultegra hub started slipping a little every 2 pedal turns. my assumption is that it's one of the spring-loaded teeth in the freewheel mechanism (sorry i don't know if they have a technical term). maybe the tooth is worn down/broken? more likely i would guess the spring broke..? is this repairable? worth the cost? able to be done myself? is it even what i think it might be? thanks.