diba sabi if you have a high mileage car then when you used a fully synthetic oil eh nagkakaroon ng leak, saan usually nag leak? I know one place is the valve cover gasket, san pa yun iba, yun oil seal san ba yun? thanks
Crankshaft seals, valve cover seals, oil filter seals, possibly valve stem seals if they're also worn, etc. Any particular spot in your car that's leaking?