iNeon,
How about that the diesels run off Vegetable oil as an advantage to the general public? There are virtually no green house gasses, home grown domestic fuel stimulates local economies, and Biodiesel iand SVO have huge positive energy gains (see http://www.mda.state.mn.us/ethanol/balance.html ) to negative gains for petroleum fuels and small energy gains for Ethanol, Plus, most spark ignition engines wont off ethanol without reprogramming computers/adjusting timing from what I understand. 20 - 30 mpg off of Veggie oil is better tha 40, 50 or 60
mpg off of gasoline.

Speaking of newer diesels, my 1998 Jetta TDI gets 52mpg on petroldiesel and 46mpg on Biodiesel. Compare that to my mother's "fuel efficient" 2001 Toyota Corrolla that gets a mere 32 mpg on Gasoline and wont run on renewable fuels at all except for 10% Ethanol as all gas cars can do.

So old MBs can still offer benefit to society if you run them off of veggie oil (biodiesel is just veg oil put through a chemical reaction so that is included here) and also remember you are saving resources by not buying a new car and making use of the old car you have. Efficient use of resources is the only way.