Not sure, whether this helps or contributes.
A while ago I noticed an imperceptable trickle of freshwater running on the starboard side into the middle portion of the bilge. As it had not been raining for a few days I suspected a leak in the water supply system. However, it seemed to originate higher up from behind the fridge/icebox and since I had not been running these, the only source could have been from under ceiling/deck/hull joints.
I checked all shroud exits below and could not discern any telltale signs. Also, one would think that these would leak earlier, ie. immediately after rain.
Then discovered that the mast ( Charleston furling) was still holding some rainwater, upwards from just below the vang fitting. Also, a couple of the vang fitting rivets showed some minor rust streaks. Siphoned this out and the trickle from the mast base onto the deck, and into the bilge as well, stopped.
Afterwards, I siphoned this water after every rain. This seems to have stopped that annoying trickle into the bilge. As the siphoning became a bit tiresome (about a bucket full), I drilled a pinhole next to the vang fitting - away from wires in the front section of the mast and not too low to interfere with any mast base sealing. This seems to drain nicely.
I really don't know the rationale behind all this, except that water may have very slowly trickled thru somehow from the higher section of this ready made rainwatertank inside of the mast, entered the ceiling/deck space and run along the underneath sides of the deck to then run down into the bilge. There was no moisture underneath the compression post.
Since then, to complicate the issue, with a new pair of glasses I noticed the absence of any apparent sealant in the spaces of/below the 'beauty plate' of the starboard lower f'd shroud. Sealed this. Whether this contributed to the leak?
Since all this work we haven't had any sustained hard rain periods and I hope that it will still remain dry when those re-occur.