As promised, I came up with a simple solution for the sagging rear diffuser. On 2005-2006 GTO's the problem presents itself like this: (Thanks, Rabs, for the pics since I forgot to take before pics of mine.)
As you can see, the problem is the black plastic diffuser is sagging at the rear flap that allows you access to the trailer hitch mount points.
Here's the materials I used to solve the problem. It's 1 1/4" x 1/16" flat aluminum and plastic push pin retainers for a 5/16" hole (similar to what holds your radiator cover on).
I first took out the push pin retainers that hold the little flap closed. With the flap now open, I measured and cut a piece of the flat aluminum to fit just inside the flap. I then drilled 3 holes in it, starting with one in the center and then one on each side about a half inch in from the edge:
Using the holes I drilled, I clamped the flat aluminum to the top side of the flap and drilled through the plastic to match the holes in the aluminum. Then I simply secured the aluminum using the plastic push pin retainers pushed through from the underside:
Then you simply close the flap and put in the factory push pin retainers that hold the flap closed. If the flap still sags a bit in the middle, simply open it and slightly bend the aluminum so that the diffuser is even with the rear valence. From the underside (if you care), you only see the heads of the three new pushpin retainers.
And here's the result:
Linear Mode
