So I upgraded to the 09+ Shark Fin Antenna. It not only looks better, but I get better reception.
Here is a link to the part numbers.
ALL YOU NEED IS THE 20815152 and the paint coded antenna. Eg.... 20815152 and 41U Black Raven would be 25831355.
Here is a Power Point link. It is for a CTS so it is a little different than ours. See my install notes below.
The Power Point is confusing as to the part numbers so remember ALL YOU NEED is the paint coded antenna from my link and the 20815152 Base.
Now on to the install.
There is a 7mm (9/32) bolt holding the rear side pannels on under the Airbag badge. The badge just pops off with a pick tool. I suggest you pry from the bottom in case you gouge it a little. Then pop off the rear lamp housing. It just pops off. Pull from the edges. Then there are 2 10mm bolt holding the "Jesus" handles on each side and remove them. The access pannels just pop down to get to the bolts. Then push the headliner forward a little to release the pop tab that holds it to the roof. Pull down the headliner and remove the 10mm bolt to release the Antenna. Unplug the color coded plugs with a jewelers screwdriver to release the plugs and take off the antenna. The hardest part is that the current hole is 1" round and the new antenna has a 1" square. I used a Dremmel and finished it with a file. There is a small alignment hole that will need to be filled with silicone. I filled the hole and put a little around the now square hole to both seal the antenna and the paint to keep it from peeling or chipping.
On to the Pics!!