You would be surprised how easily moisture can get in. You leave your watch in the bathroom while taking a hot shower and steam works its way in, etc. A C series is now a few years old, gaskets wear out on the crown tube, at the crystal, etc.Obviously your preference is to find the part and have a standard watch smith service it. If not say hello to your AD. If you have never had the watch serviced than it is time. But be forewarned your AD will charge you at least $400-500 on the service. They won't take a watch in for repair without providing a service since they are supposed to provide a 1 year guarantee.