When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
That piece has been the "what is it?", SO many times!!
It slips on to the radiator shroud, right over where the hose from the radiator to the expansion runs under the shroud. It's there so the shroud doesn't "chaff" the hose. Unfortunately GM didn't think to glue it in place....
Pleased you found it. Mine was long gone before I bought the car 7 years ago. I just cut a piece of back rubber tubing I had down the center and fit it between the shroud and the hose. Works great but probably not a fix for the purist.