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 WarningRemoval Procedure
Warning: Refer to Approved Equipment for Collision Repair 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 Disabling and Enabling.
Disconnect the negative battery cable. Refer ...
Navigation
OnStar navigation requires the Directions and Connections service plan.
Press to receive directions or have
them sent to the vehicle navigation screen, if equipped.
Destinations can also be forwarded to the vehicle from MapQuest.com.
The OnStar mapping database is continuously updated. For cov ...
Vehicle Access
Specifications
Door Lock/Indicator Schematics
Door Control Module Schematics
Release Systems Schematics
Fuel Tank Filler Door Lock Actuator Replacement
Preliminary Procedure
Remove the fuel tank filler housing. Refer to Fuel Tank Filler Pipe Housing ...