This forum has been very helpful to me with a variety of posts, so I thought I'd give back a little bit. My transponder cover looked terrible - dingy gray and dirty. So I tried staining it. It looked even worse.
So, without thinking too much about it, I found the part locally for around $10. When I got the part, what I found out was that to install this part, you had to disconnect the transponder wire which runs behind the instrument panel. A couple of posts on SLKWORLD confirmed what I was seeing with my own eyes. Hours of work! I called a couple of dealers, and found that the transponder is not VIN coded. I deduced that this meant that it is basically just a little radio that doesn't care what data it is transmitting. The destination takes care of the decoding. This meant that I could probably cut the wire and reconnect it after I switched the cover.
Snip. Now I'm committed to this.
The first thing I tried was to use plug connectors. Bad idea. They were too bulky, and it was going to be more than difficult to get them plugged together, because of the shape.
Much better idea. Who needs a plug on a transponder anyway, amirite?
I connected it without too much trouble. Notice the shielding to reduce electronic noise.
Then I finished the installation. Pretty nice, don't you think? I went with black.
Then came the moment of truth.
Success! It works!
And that's how you save yourself several hours or several hundreds of dollars at the dealership. I hope this helps someone.