I've got a riveted aluminum boat and when I bought it the seller told me that any riveted boat will weep a little. He had painted the outside, and installed a small bilge pump and it works fine. Since I was expecting it, a little water is no big deal. I did use some epoxy on a couple of the rivets that looked a little loose and that did seem to help.
Recently got a great deal on a fiberglass boat from a buddy. He'd had it for years without leaks but it had started weeping so he wanted to get rid of it. I found some scratched areas and tiny holes that I patched; also installed a bilge pump and now I feel a whole lot safer! I did some research and it turns out that boats sink because they fill up with water (guess that's not too complicated a concept is it)
and that it is recommended that all boats have a bilge pump, even if they "don't leak."