I assume you sold the manifold in "as is" condition after making a good faith effort to assure it was serviceable. He's trying to hold you responsible for his mistakes, and/or his machinist's errors. Tell him to go whiz up a rope!
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!