Chris:

MB badges the car lines by engine displacement, so a 240 has a 2.4 L engine (as originally sold). A number badge in addition indicates a different engine -- for instance, a 300E 2.8 has the 2.8L M104 DOHC instead of the 3.0L M103 SOHC six.

The "real" identification is the chassis number -- W115 in the case of your car, W123 on the 1977-83 240D and 300D and 300D turbodiesel. Cars badged 300SD from 197? to 1980 are W116 chassis cars, from 81-85 and the 300SDL to 87 are W126 chassis cars, etc.

500,000 miles on a well maintained 240 isn't unheard of. Most important thing is to protect them from internal water damage from leaking windhshield gaskets (front and rear) and leaking side window seals. Once water gets into the interior, they RUST.

The drive trains last forever with proper maintenance.

__________________
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!