I few years ago I have a 14' Naden aluminum that had a slow leak near the rear of the boat. Just a typical slow leak that plagues lots of alum boats...
I went to Home Depot and bought a few gallons of Top Cote by DUCAN.
http://www.ducan.com/deck-coating/catalogue.php I bought the Sandy-beige color (part #Part No. 160-51204). Its a thick rubberized deck sealant that has chunks of rubber built right into the liquid.
I degreased the entire inside of the boat, and took some gritty sandpaper and roughed up all the surfaces. It look me about an hour and half to prep the interior of the boat.
I then applied two thick layers of the Top Cote. I specifically lathered on extra Top Cote around all the seams and corners.
Once it dried, the boat never agian leaked a drop, it looked really good inside, and i no longer had problems with the slippery aluminum bottom. It cost me about $90 to do this.
That all being said, if you have visible gouges/large hole etc in the aluminum this will not work. But for the slow leaks the material fills everything in very nicely.