1986 W124 300D Euro model. This car has the NA 3L i6 paired to the 4 speed auto.
I've gotten close to 40MPG on long trips with no traffic and doing a steady 70 - 75MPH on fairly flat surfaces.
I also do a LOT of city driving in and around NYC. I've never seen my mileage dip below 27, and this includes winter time.
I recently started recording my mileage on
www.fuelly.com and over the last 4 fill-ups I've averaged 30.4MPG.
You can check out my averages and statistics here:
http://www.fuelly.com/driver/s38junkie/300d