I have a 1987 300SDL with 39,000 original miles. We are the first
owners of this car. It is in perfect condition garage kept. We want to
sell it and i'm not sure where to get an accurate value of it and
where would be a good place to market it.....any ideas?

Ebay will bring the audience to your car. Since it is such a low mileage...
with proof as in service records and carfax, you can ask as high as you want
to... Maybe you might get $9000 for it... maybe or maybe not...