Anyone know how this little guy goes together. The rotating flapper has two tangs which snap into place but I sure can't figure out how to do it. <br/><br/>Here's how this problem came up. The small vent to the left of the driver was missing the flapper. <br/><br/>When I was installing my windshield shade the little mounting pin on the end of the shade slipped out, bounced on the dash and...