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 WarningInstallation Procedure
Remove rear end upper panel extension (1) from service part.
Cut
Cut the body side inner panel in corresponding locations to fit the
remaining original panel. The sectioning joint should be trimmed to
allow a gap of one-and-one-half-times the metal thickness at the sectioni ...
Engine Exhaust
WARNING
Engine exhaust contains carbon monoxide (CO) which cannot be seen or smelled.
Exposure to CO can cause unconsciousness and even death.
Exhaust may enter the vehicle if:
• The vehicle idles in areas with poor ventilation (parking garages, tunnels, deep
snow that may block underbody air ...
Installation Procedure
Clean and prepare the attaching surfaces for welding.
Apply structural adhesive to the attaching flanges.
Position the body side outer lower panel on the vehicle
Verify the fit of the body side outer lower panel.
Clamp the body side outer lower panel into position.
Spot ...