I doubt that "bad valves" would cause your engine not to start unless the camm belt has snapped. They don't all go bad at once. Have they tried a new camm rotation sensor? It seems easy to flood these engines and the oil may have washed off the rings. Be sure he's squirted some oil into the cylinders before doing any leakdown test. Are there any signs your coolant is contaminated w/ oil or have you been loosing coolant?