Have you had a look at the packing gland? It shouldn't be leaking when the prop shaft isn't turning. If the boat has been tied to dock for a long time and hasn't be sailed or motored water may not have made it's way into the bilge. Just taking it out for a sea-trial could either start the packing gland leaking or letting trapped water move into the bilge.
Oh and by the way welcome to the most knowledgeable sailing group on the net.
Oh and by the way welcome to the most knowledgeable sailing group on the net.