I might suggest that your asking price is a little on the high side.
I ran the Kelley Blue Book value for private party retail and used my zip code in Southern California, where Mercedes Benz prices are probably higher than in North Carolina.
It came up with $22,215, adjusted for mileage and "excellent" condition.
http://www.kbb.com/kb/ki.dll/kw.kc.ur?kbb;048997;CA037&;p&722;Mercedes-Benz;1992%20300SL&11;MB;A3&
If you can get more than that, then more power to you, but a person getting a loan to buy your car will not be able to pay more than Kelley Blue Book value for the loan.