If you can get the failed sealant out (use good quality paint remover and give it time to work), just tape over the pinhole(s) and use Caswell epoxy tank sealer. It not only lines the tank, it also strengthens it in the process. https://www.caswellplating.com/epoxy...-to-5-gal.html
Keepin' all the left over parts. Gonna use 'em to build another bike!