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 WarningWaterleak Test Preparation
GM vehicles are designed to operate under normal environmental
conditions.
The design criteria for sealing materials and components takes into
consideration the sealing forces required to withstand the natural
elements. These specifications cannot take into consideration any artificial ...
Installation Procedure
Drill 8 mm (5/16 in) for plug welding along the edges of the drivetrain
and front suspension frame front support as noted from the
original panel.
Clean and prepare the attaching surfaces for welding.
Position the drivetrain and front suspension frame front suppor ...
Installation Procedure
Drill 8 mm (5/16 in) for plug welding along the edges of the body side
outer lower panel as noted from the original panel.
Note: If the location of the original plug weld holes can not be
determined, space the plug weld holes every 40 mm (1½ in).
Clean and prepare the attac ...