For service and parts needs, visit your dealer. You will receive genuine GM parts and GM-trained and supported service people.
Genuine GM parts have one of these marks:

Vehicle Care
California Proposition
65 WarningValve and Seat Grinding Seats
Valve Measurement and Reconditioning OverviewProper valve service is critical to engine performance.Therefore, all detailed measurement procedures must be followed toidentify components that are out of specification.If the measurement procedures reveal that the valve or valveseat must be recondition ...