Your mechanic is a big idiot leaving engine runing for long after overhaul is at best piston ring torture
Also you were not vitcim of fake oil as you thing you were victim of no t.vavle with your engine running dead cold all the time you wasted all your money spent on engine oil
Also it is a very good pratice to change oil ventilation rubber pipes every two years as they tend to get hard as plastic (hard rubber pipes will reduce engine oil life) these rubber parts are dirty cheap not more than 200rs in market