Mike, I, too, rebedded my cowl as the "obvious" first step. Thought the leak was stopped because the water stopped dripping. That first rebed was at the Roche Harbor Catalina Rendezvous in May 2017. Les Troyer and John Shepard were great helpers. In fact, they were so enthusiastic that I watched them gather the tools (long "blade" on John's power drill, Les working out the butyl tape I'd supplied), that they had the work done before I could ask them to stop and let me even try to help!
The leak, which manifested itself by drips through one of the three screws holding the trim ring in (I removed the ring and saw a smaller version of your cracks), stopped for awhile, only to reappear (when it started raining again). I tried that again; definition of insanity, right?
Then I did the traveler track. Stopped, but then it rained, showed up later in the winter and early spring.
I saw Les again in early April this year, demanding my money back as part of the warranty!!!!!!
We both laughed.
He and I traced it down to the fairleads for some of my aft led lines that run back to the cockpit (two small bullet fairleads, small screws, but could be).
The only other thing above that hole inside up on the deck is the hatch wood trim.
It's been dry here for months, no drips. I can readily believe your results with the hose, but my experience was it took longer to reappear.
I was tempted to just slather Marine Tex inside and stop the drips, but, like you, I want to find the source and stop that.
That's where the link I posted could come in handy.
With my luck, I'll get around to doing that work only once it starts raining again! Just like when I rebedded my saloon hatch!
Good luck, please keep us posted.
