I had a similar leak on my FW tank. I have two 40 gallon FW tanks that are connected by "equalizing" hoses. The leak turned out to be simply a loosened hose clamp on one of the 1" equalizing hoses. Just a few turns of the screw on the hose clamp and the leak was fixed.
I think you need to really take a good look at your tanks before assuming something is wrong with the tank itself. While that may be true, a loose fitting is a much more likely suspect. As others have said it is highly doubtful that the small amount of water left in the tank to freeze overwinter would cause a crack in your FW tank.
