How To But A Floor In A Aluminum Boat Leaking Aluminum Boat...center Keel?

Leaking aluminum boat...center keel? - how to but a floor in a aluminum boat

Boat (12 ') has a leak, when the sides meet the floor at the front ..... small crack (1 / 4 inch or less) at this point .... seems that an original cap or a plug in the gap, which may have been in place by a screw or held?
Is there a replacement or to fill the gap or not?
Thanks