$&$*# leaks are always a pain. Can you be more specific as to the location?
I suppose it's either coming in from above or below. You in saltwater? Is it salty?
I have a Catalina 309 and we were getting water in the boat. Occasionally coming off a big wave, water was forced up through the seacock and out the sink drain in the head. Collected on the countertop and migrated past the bulkhead and collected on the ledge above the dinette. Took a couple days to figure that one out. We just keep the seacock closed, now while underway.