If you don't insist on GM Collision Parts, you could get stuck with cheap imitations. GM recently released a Parts Testing report comparing GM-produced replacement parts to aftermarket parts.

The tests show that the non-OEM parts don't measure up in the materials used, their assembly, or fit.

 Collision Technical Repair Information
 GM Collision Parts Testing Report (PDF)
 "Your Vehicle is an Original" Brochure (PDF)
 "Your Vehicle is an Original" Brochure (PDF - Spanish Version)

You must have Adobe Acrobat Reader installed on your computer to view the document files above. If you don't already have this program, you can download it free at www.adobe.com.