The perfect Diesel would be a 1986/87 300SDL -- tons of room, very reliable, decent performance, and excellent milage. There is one for sale at the small lot near the lab (they handle many of the local trade-ins from the dealer), asking 8995, but it's been there for weeks and will probably go for less.
My borther bought one two years ago, and all we've done to it is change oil, change a blown (corroded) climate control fuse, tires (died of old age) and a set of rear pads because the pedal was getting hard.
Has 150,000 on it so far....
Look around, they are out there, and can be had for decent money. Check the coolant tank for oil -- cracked heads are the only real problem.
The 81-85 300SD is the same except for trim, headlights, and a shorter rear floor pan, and it has the 5 cylinder 617 turbo rather than the 603 turbo diesel -- still a very good car!
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!