Just an update, the final culprit of oil leak was the axle seal from left side wheel. It got fixed on third time (and after I went to a different mechanic.) It turns out, my old mechanic was installing lancer seal which was slightly more wide. No more leaks, at least for now. The new mechanic did fiddled with tappet though and I am thinking of taking the car for computer tuning some time soon. But for now, it's good.