@porfin, speaking for the vents or dorates. My '77 Columbia 8.3 has two and water does get in one of them.
We've got two (one each to port/starboard just aft of the mast) and they work pretty hunky dory for us. The starboard one is in the head, and the port one is at the aft end of the forward berthing compartment. Keeping the two cowl's facing in opposite directions (preferably one into the wind and the other 180* off the wind) gets a nice cross ventilation going due to the Venturi effect of the cowl facing off of the wind.
Interesting that one of your leaks, but not the other. That would seem to indicate that your dorades are not undersized for the cowls. You may want to take a peek inside the dorade box to make sure there's nothing stuck in there or otherwise amiss. It could also be that the bottom of the cross piece is no longer sealed to the deck, which kind of makes the design OBE. Of course, they're not gonna take a lot of green water without leaking, but should be able to handle rain and spray.