The best product mercedes ever delivered was the W201 190D.
This simple 4-cylinder diesel just goes on and on. We have 2 liter diesels of this model with more as 1.000.000km and still no problems.
The W124 had the same engine in Europe, but since the car is a lot heavier, these engines tend to brake down easier (after 700-800k km).
The 5- and 6-cylinders never drive that far without head or head-gasket problems.
The later C and E classes have to much electronic steered components (such as the fuel-pump) and need a lot more maintenance.
As far as I am concerned, the 190 Diesel is simply the best and there is no gas-burning engine that can even come close to the endurance capacity of this little diesel!
And besides, mercedes produced the W201 190 from 1982 till 1993! Eleven production years for such a daily-used car...must be a good one then...
with a minor 600+k