Pablo, you need sik-a-flex. The tinny owners best friend. I do my boat every couple of years and my tinny was first purchased in the 1950's and has seen hard use. I use a wire wheel on my cordless drill along the seams, then run sik-a-flex along those same seems, all is good afterwards. Seal-All works well too. on a single leaky rivet that is.
sik-a-flex is about 14 bucks/tube and lasts for about 3 years but your mileage may vary depending on use. You can buy it at a few places but Capital Iron always has it.