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
Cut the roof front header 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
sectioning joint.
Create a 50 mm (2 in) backing plate from the unused portion of ...
Removal Procedure
Warning: Refer to Approved Equipment for Collision Repair Warning in the
Preface section.
Warning: Refer to Collision Sectioning Warning in the Preface section.
Warning: Refer to Glass and Sheet Metal Handling Warning in the Preface section.
Disable the SIR System. Refer to SIR
...
Front Side Door Upper Hinge and Lower Hinge Replacement
Preliminary Procedure
Remove the front wheelhouse liner. Refer to Front Wheelhouse Liner
Replacement.
Remove the front fender insulator. Refer to Front Fender Insulator
Replacement.
Remove the front side door. Refer to Front Side Door Replacement.
Front Side Door Hinge Bolt ( ...