I have seen this type of issue when my sons would use my metal mag-scraper. When I reached in the tank to feel it, the scraper had under cut the seal and tore holes in it.
Good news, the tank seams where glass hits glass don't fail often, and you can actually cut the inside seal, clean, and reapply silicone without having to completely cut the glass apart. They even make special blades for the job. I wouldn't worry about such things until you see an air bubble between glass contact points*and* that particular seam has a damaged seal.