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 WarningRigid Plastic Part Repair Materials
Rigid Plastic Part Repair MaterialsThermoset Plastic TypeType of RepairRecommended Repair MaterialAvailabilitySheet metal compound (SMC), RIM rigid plastic partsCosmetic fillingGM Goodwrench® Structural Bonding Epoxy (GM P/N12345726 or equivalent)GM DealerSikkens Polystop LP™ or equivalent polyes ...