I would suggest that water intrusion is not something you can count on seeing. With a cast iron keel(?) unless properly dried, sealed and covered, it will continue to rust and cause major problems down the road. If the rudder has a foam core, water has intruded and the foam will deteriorate as time goes on, under the repair.
You basically have 2 choices. If you like and want to keep the boat, have a surveyor do his thing and then follow his advice. This may require a boat yard to do the repairs. If you really don't care about the boat, cover up the damage any way you please and plan to sell it within a few years.