Richard, the dealer, with knowledge of the noise is giving substantially more than the figure you note (and yet a lot less than what the car would be worth to you or me). I have shown the car several times to individuals some of which did not care about the noise (even though it is prominent and evident) -- the car shows that well. I am of the belief that the dealer would offer the amount offered even if the car was in showroom condition -- that is the nature of that business -- make money on the sale of their car make money on the purchase of your car. If you walk into a dealership to buy a car they figure they are entitled to make money on both ends.
I am neither new to cars or to Mercedes Benz. I know the value and I know how dealers operate. I guess I will ascribe the loss that trading the car into a dealership represents to the joy I have had in the ownership of that car -- it was worth the price, and it is probably worth it to leave this car before a series of major repairs, that will surely come due, sour that joy. The car has been costly but fun and I realized a long time dream of ownership of a 560SL. If anyone wants a beautiful 560SL for a very good price let me know quickly.
