[DavidG]

Sometimes all the adjustment available isn't enough. More than once I have had to slice one like a loaf a bread into two cowl vent gaskets (only one of which is usable). The problem with most of the reproductions is not just their thickness but density of the rubber. When they're too dense, all of the adjustment (and added pressure by temorarily adding some heavy weight on top of the cowl vent ) will make a dent, but sometimes it isn't enough to end up with the top of the vent lid flush with the rest of the cowl.