Do you have "Elephant Trunks".
One of it unglued or been not glued properly and it was source of small like for me.
When boat shakes on mooring or use on the water a small amount flows through this pipe.
Identify is very easy. Move these trunks up, enter garden pipe into enter of the pipe from boat and observe if you have any leak in Elephant Trunks.
I have made small path will test after winter again
Please find on mentioned below picture source of mine "problems":