Permatex Ultra Black is not the primary seal in our Water Neck Adapter. The primary seal comes from the silicone seal inside the adapter compressing into the taper of the water neck. We use Permatex Ultra Black during installation because it helps lubricate the seal as the adapter is tightened, allowing it to seat into the taper without binding or bunching up. It also gives us an added layer of protection by helping fill small imperfections that can be present in the surface of the water neck. Once it sets up, it does not stay permanently slick the way grease can, which is another reason we prefer it for this application. The adapter is still designed to seal mechanically. The Permatex is there to help the seal install correctly and provide an added measure against minor surface imperfections. Patented AutoPlumb Water Neck Adapter Shop at AutoPlumb.com #ANFittings #CoolingSystem #LSswap #HotRod #CarEnthusiasts