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 WarningLicense Plate Lamp
To replace the license plate lamp bulb:
1. Remove the two screws from the license plate lamp assembly.
2. Turn and pull the license plate lamp assembly down.
3. Turn the bulb socket counterclockwise and pull straight out of the lamp assembly.
4. Remove the bulb by pulling it straight out of ...
Installation 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 ...
Anti-Corrosion Treatment and Repair (Base)
Warning: When applying sound deadeners, or anti-corrosion materials
due care and preventative measures must be exercised to prevent
any material from being sprayed into door and quarter panel mechanisms such as
door locks, window run channels, window regulators and
seat belt retractors, as wel ...