Mate, that's a good idea. I always think to myself why does Pakistan not take advantage of diesel cars like we do in the UK. Most of the cars at my home back in England are diesels. Diesel engines just tend to hold out better and longer than peteols, not to mention how much better they are on fuel economy. What yr is your E Class? E220 past 59 plates do north of 60mpg, which is great for a luxury saloon.
HOWEVER. What you'd be saving on fuel over time, you could well enough end up loosing in trying to find a diesel specialist to maintain or repair the car if ever required. I bet most mechanics wouldn't even know how to access the engine itself under the engine cover/panel that's fixed onto the top of it haha!... So for that reason it won't be such a good idea. But i guess unless diesels become commonplace in Pakistan, it will always be difficult to find a reputable diesel mechanic. I call this the 'Laal CD70 syndrome' because whenever someone goes to buy a bike, he'll buy a red cd70 thinking its a safe bet because it'll be easier to sell. This just happens over and over and over again and its just a chain reaction: everyone's doing it! We need to change this psychologic mindset in Pakiatan somehow before we can see imports become more common
P.S. I myself was actually thinking quite seriously last year to sell my Honda CITY and import a VW Polo BluMotion, i worked it out to cost around 18-19 Lac all in. I wanted to import that specifically because the new shape Polo does a whopping 90MPG!! But I've backed off the idea now