It sounds like the machine shop didn't put enough clearance in the guide when they installed the valves. Yes, take the head back to the shop- - - -if they're reputable, they should fix it free, and provide you with a new gasket set. Any shop I've owned or managed would handle things that way.
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!