I think the problem will lie in the way that the hat channels are added into the finished hull layup. They'd be a cold joint and the geometry of the channel is susceptable to peeling failure from the inside of the channel. (Peeling is the usual failure mode of tabbing and similar laps.) Like I commented on my similar scuppers, I fear that water can sit in there below the hull opening and freeze; if so and if there's enough volume trapped then the freezing would be pushing against the very substantial hull and pushing against the inside of the hat. That pressure would tend to peel the hat away from the hull. One could expect that your closure is much the same (where mine just ends an inch or so below the opening), and your hat is continued on past. Perhaps you can see a 'bobble' in the way the 'glass is laid up?
Repair doesn't seem too tough. Having proven to myself that water leaks out from the bottom of the passage by perhaps heeling the boat on a calm, flat day, I'd probably squirt solvent through the crack (thinking all the while about flammable vapors trapped in the bottom of the hat) and pour neat, then thickened epoxy to fill the crack. For me, the hardest part would be getting the inside of the thing clean of bottom paint.
I imagine that all your frames have limber holes at their bottoms?