a good synthetic can cure very minor leaks and decrease amount of oil burnt. If you're burning/leaking a quart a week then there's pretty much no hope.. but the higher quality oils can cure minor issues.Not 100% sure, but I was under the impression that if an engine were leaking oil, synthetic oil would just leak "better". If the engine is burning oil it's not a good to use synthetic either (probably a waste in terms of cost). Sometimes high mileage engines are prone to those problems. I still need to look into that...