I don't know if you have the manual for your boat. Here's the link.
Only read after a good sleep and a cup of coffee, the plot is not very engaging
Anyway, there is a description of the trunks. They have a non-return flapper valve within them. Worth checking if they are operating correctly and sealing, thus avoiding reverse flow and water ingress into the bilges from the sea. One of them may be worn or simply compromised by foreign matter on the sealing surface.
There is also a schematic of the hull. I'd start at one end and work through what the manufacturers installed in terms of bungs etc.
Then see if any "improvements" were installed by any previous owners the boat had.
Hope this helps you.