General Motors used to recommend a specific sealer for leaky carb castings back in the 1980s- - - -something that usually happened after a rebuild when certain dip cleaning chemicals were used. Apparently, they had a run of bad castings that needed to be sealed to prevent leaks, and the dip cleaner would dissolve it. I don't have any idea if it's still available- - - -probably not. Some of the stuff we used back then can have a bad side effect on the environment- - - -they'll make your kids be born naked! Jon (Carb King) might know something about the casting sealing process.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!