318 2bbl carb replacement

I got this knock off carb . It has a Chanel under it for looks like a O ring type gasket ( see photo ) . The older eBay carb that on it doesn't have it though they look nearly identical otherwise . Does anything need to be put in that Chanel ? This carb was sold to me from Napa as a stock replacement for 73 318 challenger . But Original didn't have it and neither did the ebay carb