Suggestions:

If you are looking for a high "volume" exposure net ad, I've seen that autotrader.com list vehicles US wide.

Naturally e-bay holds "volume" exposure as well.

In SF there are "SL" automobile sales specialists/companies. You may wish to consign your car, and cut a little $ of the sale over to them.

You may wish to take an ad out in your local MB Club, or Star Magazine too.

Also, there usually are smaller local newspaper/periodicals that cater to the "higher per capita income" city areas....(they do exist here in SF)

If your vehicle is truly a perfect "10", you may also wish to list it in a high end mag ie. the Robb Report, Dupont Register, etc. (world wide distributions).

More suggestions,
>don't be too desperate to sell the vehicle, a "motivated" seller would be the politically correct stance and hold a healthy frame of mind through the process
>if worse comes to worse and you are unable to sell it, maybe its your karma to keep the car.....have a wonderful life (maybe negotiate with your significant other). We all make a few sacrifices to have one or two things really really nice in our lives
>favor picture ads, it speaks volumes
>take a drive for brunch/ coffee and park the car on Sat. and Sun in the best areas (with a for sale sign w/ related info on it)- preferably fully detailed...you may also employ this strategy and park it in front of the MB dealer, Jag/BMW/etc. (if you are so bold enough).
>if you have a network of individuals inclined toward an "SL" type vehicle- - contact them: car enthusiasts, professionals, current SL owners etc. (I've encountered a few retired individuals and regular folk interested in owning the car they have always dreamed of and had the ability to pay $$$ too)
>maybe your fiance has outlets to advertise the availability of this vehicle too ie law firms, big companies, accounting firms, etc.

Good Luck and hope this helps.

-fad