diesels are very long life engines, and require less maintenance than their petrol cousins - the problem in Pakistan is ustaadjee trying to milk money from the owners, they have one gauge of diesel engine health, "backpressure measured at idle" Its wrong - they judge oil by its color and slick between fingers, its wrong.. You need proper analysis tools to determine a problem.
Yes we have old diesel technology at hand but that does not mean its doomed to be smoky etc, in correct tune it will be silent and clean. The newer DI engines have more torque and less noise but have a number of added technology which our ustaads dont understand and our owners do not want to spend money on correct diagnosis, their drivers are their best service advisers who then pour API CE grade oil in them and wonder why their turbocharger bearings gave away, they blame fuel quality etc etc. while the fault is their own.