I've got a 30 gal that I picked up for cheap that is kinda old. When I got it it was leaking so I resealed the whole tank. This was about 5 months ago and it just sprung a leak about 2 inches from the top. When I fix this do I have to scrape out all of the old silicone(which is only about 5 months old) or can I just fix the section that is leaking?