It seems a lot of these old mercedes diesels get better the more you drive them but i have noticed that fuel quality plays a part too . if the car smokes and everything is adjusted properly, try buying your fuel somewhere else. I once bought a tank full of fuel and within 20kms the vehicle was smoking really heavily . It turned out later,that owner of the gas station had been buying used turpentine and was adding it to the fuel . He was prosecuted for this .