I believe the only place that salt water could enter the boat and settle aft
of the aft waterproof bulkhead is through the rudder post assembly. I suggest
that you check that area while sailing. You should also carefully confirm that
the water is actually salty seawater and not just fresh water that has
sloshed around the bilge. It is often easy to confuse one for the other.
S/V MALAIKA II