We picked up our new, 2010 Tour 42AD a couple months ago after the coach had been on the lot for quite a while (about a year). The coach has subsequently been great and we have had very few issues (did get a very complete pre-delivery service). Still, I noticed the exhaust deflector looked very rusty.
We had a 2008 Tour with the same deflector before, and I knew that the "rust" was actually a fuel residue, so I finally got out the metal polish and tried to clean it up. Wow -- that residue is tough!

I then tried some 400 grit wet sandpaper, but it clogged up immediately. So, in place of water, I tried using a little WD-40 with the sand paper and that worked great. This combination allowed me to remove the residue, and clean up the deflector (with no scratches). I then used the polish to finish it up with almost a mirror finish.
If your deflector is looking a bit sad, you might give this a try.