I just had a new roof installed, suprise, I now have a leak on my upstairs bathroom ceiling. My roofer insists that it is the bricks and/or mortor joints that are leaking. He may be right, because when he covered the chimney, the leaking stopped. Anyhow, I was told that if I waterproof the chimney with sealer, it would stop. Is this true, if so what product would you reccommend, and how should I apply it? Thank you.