Permatex makes an Aviation sealant(WORKS WONDERS) we use some of it at work, so I picked some up at the local O'Reilly's. comes in a white container with a brush in the lid. It is good for all fuels, coolants, other chemicals. I guarantee it will seal anything or I will send you the money for it!!!!
Aviation Form a Gasket FTW!

Really good stuff.