After too much rough handling over the past 20 years, I am getting a seeping-type of leak along the keel of my aluminum canoe. The leak seems confined to the last two feet in the stern. At least, when I look down I see water slowly spreading out from the center line of the boat (where the keel is attached by a double row of rivets through the bottom and then to a 2" wide aluminum strip that runs the length of the canoe), beginning about under the rear seat and extending back from there. My guess is that years of banging around have loosened the rivets. Any ideas on repair options?