My guess is you are getting leakage from your opening ports frames. The gray rubber or plastic seal between the lower and upper aluminum frames do break down over time and leak. I had a 1988 Catalina with the same ports, but with black seals and they never had a problem. I assume the blacks seals are more resistant to UV. When we got our 1999 C36 most of the opening ports leaked. The gray rubber or plastic seals had deteriorated and became very soft almost like putty. I used a dental pick and cleaned out the old seal and caulked the joints. Leaking stopped. I had initially thought the o-ring port seals were at fault. The black seals on the Catalina 30 were still quite firm and tight when we sold the boat a couple years ago and never leaked.

This may be the source of the water that is getting into your core below the ports. This area around the ports may not actually be cored. I don’t think it was on the Catalina 30. There was a space between the exterior fiberglass and the interior liner.

I have a friend with a Beneteau with the same ports and he had the problem and fix.

Rick- you may want to survey the suspect area with a moisture meter if you suspect any hidden water.

Rick,

I have been fighting a leak not unlike yours on the side of the house. I noted that one of the screw holes at the point of the eye brow trim strip ( I removed my eye brow, thought it made me younger looking). Occasionally if I press on the side of the house I get a small gush of water out this hole.
This is above the ports, I assume it is coming from the hand rail mount holes or from the vent for my heater just inboard of the hand rail. No leaks noted on the interior in this area.

My plan is to suck out any remaining trapped water, reverse the hose on the vacuum and hold it against the weeping screw hole while spraying a soap and water solution on the suspect areas and looking for bubbles so I can address the source.

This is if I can beak loose from work and home chores to attend on my boat, have not been able to attend to her in over a month. Varnish among many other chores await.

I haven't actually pulled the windows out of my Catalina but on my previous boat, with similar construction and age, there was no core in the cabin sides, just a large void between the deck (outer skin) and liner (inner skin). When I got a window leak water would and could travel many feet inside this void, making it hard to pinpoint the origin of leaks.

The good news was that the core in the side decks was sealed off from this cabin side section, so the water wasn't doing any serious damage.