I've had 100% success with "POR-15" sealing fuel founts. At first I used the more expensive "Marine clean" and "metal ready" products before applying the "Por-15" sealer, I have since discovered that as far as lantern founts go, Woody Kirkmans' simpler suggestion of white vinegar and sash chain cleaning method works just fine and the Por-15 adheres just as it should. As noted however, larger pinholes should be covered with a moisture proof tape until fully cured before filling the fount with fuel. As John states however, once a can is opened it must be used completely as there is no way to stop the curing process once exposed to air. I usually use 1oz. per fount in old dixie 3oz. disposable bathroom water cups, (I don't know if they are still available, these date back to the late 80s' when I bought a couple of cases of them, what was I thinking?) Nonetheless, the product works very well and is highly recommended.
Willis