Interesting thoughts. I had the same happened to me when coming back from Rhode Island. I too thought it was from the chain locker. During the passage I checked the bow thruster. Everything appeared dry. I replaced the seals earlier this spring. I checked the top of thruster and saw no water / moisture in and around the area,
The head was also replaced and no water was noticed overflowing during the starboard tack.
I did sample the water and it was definitely saltwater, so it was bot not from the water tank.
This is the first time it ever happened. Outside of replacing the seals again, what else can be done?