I've been working on resealing my new tank but I've ran into a problem. I've already scraped all the seams with a razor several times and you can still see where the silicone was. I've tried using vinegar, mineral spirits, and acetone and nothing can seem to do the job. It's a pretty old tank and it looked like someone already tried to do a not so great job of sealing it up. Could the glass be stained or do I need to keep trying? Also, when I rub my finger over it, it is smooth like the surface of the glass and not rubbery like the silicone.