I own a buzurg mercedes - she has nearto 190000 miles on it today - I bought it with about 150,000 - and Im pretty sure the previous owner used fizool and wrong engine oil and filter in it. I changed it to the shell ultra equal sold in USA with fleece type filter and the engine has cleaned itself out and the engine performs like a mercedes benz engine should. Smooth and elastic powerful.
No issues at all. I also use synthetic in my old and redone camry engine - no worries either. Its about 140,000 miles old.
for the easiest way to purchase, call shell Pakistan UAN, get a hold of someone sensible and ask where to buy it.