Pinhole leak in timber boat

[Lepke]

This stuff will stop the leaks from either side, but outside is best. Once in the seam, water can run along and come out somewhere else. Also rot issues.
A swim/dive is easier than disassembly. In the long run, the seam needs to be fixed correctly. Stay-Afloat lasts enough until a proper fix, but not meant to last forever. Video on their site. It will stop up a large thru hull.