There are two possible causes, but you will need to remove the vinyl panel to determine which one it is.
The first possibility is the rub rail screws. The second is that one of the bow railing support posts may be leaking.
Once the vinyl panel has been removed, have someone spray water along the underside of the rub rail and around the bases of the bow railing supports. This should help identify the source of the leak.
If it is the rub rail, it will require some work. You will need to remove the chrome insert from the rub rail, then remove the screws securing the black rub rail. Locate the screw that is leaking and reseal the affected screw(s). After resealing, reinstall the black rub rail first, then align and reinstall the chrome insert.
If the leak is coming from a bow railing support post, locate the stud that’s leaking and remove the nut. Reseal the base as needed, then reinstall and tighten the nut.