A 240D is a slow car, it's under powered compared to contemporary cars.
If you drive on country lanes in a relatively flat (vs. hilly) area it
will be satisfactory, otherwise, look elsewhere. 68 HP is simply too
little to accelerate a 3,300 lb car; its 0 to 60 MPH time is about 19
seconds, about twice the time of contemporary cars which are one's
"competition" on the road.
But don't blame its being a diesel, the engine is simply too small. I
suggest you consider a 300D Turbo which makes 120 HP and is, like the
240D, a simple, durable and reliable engine.
These old diesels ought to get: oil & filter change every 5K miles,
valve adjustment every 15K miles, air & fuel filters and automatic
transmission fluid & filter change every 30K miles.
Find a clean car without rust that has this maintenance history; its
engine and transmission should have a 250K to 300K useful life - deduct
its present mileage and you see how much life remains before an overhaul
will be needed. Avoid poorly maintained, beat up cars for as "cheap" as
they may be to buy they're the most expensive used M-B that one can buy.