Any silicone that is 100% silicone will work. Make sure that it is not the "bathroom" type silicone that contains an antifungal. No matter what you pick up at the hardware store they all say that they are not for aquarium use. Can't explain that, but I have used the GE 100% silicone on every tank that I needed to reseal and had not ill effects.
As far as your leak is concerned, if you have a leak that is in one of the main seems of the aquarium, I would remove all of the old stuff and reseal the whole tank. Silicone does not seal to itself well. For the integrity of the tank, it's best to reseal the entire tank. Hope this helps!
Best wishes!