I bought a 120g tank that was built in 1993. The silicon on the inside of the tank in two of the corners is kind of crumbling and pulls away from the glass easily when I run my finger down it. Should I do a leake test and leave it if it holds or go ahead and replace it while the tank is empty? If I need to replace it do I need to take the glass apart or just take the old seal off as much as i can with a razor and silicon it up?