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 WarningSIR Service Precautions
SIR Service Precautions
Warning: When performing service on or near the SIR components or
the SIR wiring, the SIR system must be disabled. Failure to observe
the correct procedure could cause deployment of the SIR components. Serious
injury can occur. Failure to observe the correct procedure
...
Installation Procedure
Align the front side door outer panel.
Verify the fit of the front side door outer panel.
Clamp the front side door outer panel
into position.
Pre-flanging the flange with BO-6396 pliers and BO-6392 tool kit .
Continue to hammer in stages along the hem flanges.
...
Paint Gauges
Paint thickness gauge. measure the total thickness of the vehicle finish. It
is important to accurately measure the thickness of the finish on
each vehicle as the thickness of the finish will vary on each vehicle. Use a
paint gauge before the sanding process in order to accurately
measure how ...