I looked at your ad in Excite, just to see what you were asking. Your asking price is $14k+ and blue book retail, from the link you have included, is $11k+.
I've met you and seen the car, so first let me say I think you're a pretty good guy with a really nice car. That's not just payback for giving me a bumper cover either.
Now, I have to tell you, IMHO, if you really want $2-3k over retail, you're going to have to have some serious patience. I picked up a pristine Volvo 765 Turbo in Tennessee from a guy in a similar situation as yours. He wanted dealer money (blue book) because the car was that clean. After extensive negotiations, we agreed to something between trade-in and retail. I hope you get your price, but as a buyer, I'm not going to offer any private party what amounts to dealer money for a used car, there's just too many of them out there. KBB Retail is for a car that the dealer has vetted and is willing to stand behind for a year or two with a warranty. No matter how nice your car is (and I will verify for the list that it is a very clean 300D), there is a risk to the buyer for taking a private party car that is not there with a dealer purchase. That risk has a value to most people and they're not going to give you more money than the dealer would get unless you've got something very exclusive.
Now comes the debate about how exclusive the 2.5 turbo diesel is and what that's worth. Unfortunatley, only serious mb dieselheads know that engine is worth more than the others, so again, you're at a disadvantage.
Good luck, I do hope you can get your price. I just wanted to give you my opinion on why you might not be hearing the phone ring as often as you would expect. Be patient. mike