Assuming that you have leaks into the side locker? It's not clear to me.
If you are feeling brave (stupid?) It is possible to climb into these lockers and lie down inside (at least at 5ft 8 1/2" tall, it is!)
I've done it, to fit new midships cleats. Your Deck fittings could be leaking, especially if they've been worked hard.
Swallow Matt has done it, and it's captured on one of his Utube vids about the BRe. Amusing!
Added. On "Swallow Yachts Bay Raider Exped walkaround" at min 30s.
https://youtu.be/fVNUU8eDmGE?si=ZrHxJobNQolRdW9pSuggest getting a responsible adult (maybe not the beneficiary of your life insurance?) To then hose down the exterior?
Alternatively, commercial devices are available (ultrasound emitters, I believe?) That enable leaks to be traced without adding more water. Good for cars, and spaces containing cargo/equipment which absolutely cannot be wetted.