I don't know what the "flap" is called...it traps the air coming thru grille on bottom side of grille....forces it to go thru the radiator. Thin rubbery material about 36" X 12".
If you can get your hands on one grill spring or take a look at one. Take it to Home Depot I got basically the identical one for under 2 bucks, GM want over 30
If you can get your hands on one grill spring or take a look at one. Take it to Home Depot I got basically the identical one for under 2 bucks, GM want over 30