Here is update.
Jameel Autos (Irshad) were really helpful.. he had a look and said engine needs tuning and asked when the spark plug was done, I told him the previous workshop (CNG guys and also the mechanic) both worked on the car and they said plugs are good. .well he took them out and they were completely gone..
He then performed compression test on the engine and even though it was smoking, he told me its fine to carry on but need to keep the oil level ... the car is dropping approx 2L every 30 days and this was back in January..
Nothing has been done on the engine side at the moment. Life keeps throwing curve balls and other things are taking preferences .. but oil leak is getting bad and the odo just crossed 280,000 (this current D15 is from 2013 and the previous owner used to travel to and from LHR so im sure a lot of these have been on this motor)
I have been looking for options and @ sherhah D15 8valve is available for 28K or 16v for 35k .. D16 with EFi conversion is ranging from 60-70k - basically out of budget.
My suspension wala introduced me to this workshop near Ayesha Manzil, ex-Honda mechanic who looked underneath and told me its not even the main seal that needs doing, the chamber, whose seal i got replaced not too long ago is leaking and oil is also coming from timing side.
At this point I dont even know who to believe or what to do.. Get the oil seals done, as many as possible and see if the leaks stop . then I can use some nice oil to prolong the engine's life.. I have a project going on which means I don't want to spend much on car for next 6 months.. after that I can do whatever I want...
Side note: What oil to use in an oil leaky engine? I have started using PSO 20W/50 and it seems the engine is smoking even at 1500 rpm..