Originally Posted by Fiero3800sc
Full synthetic keeps things clean. A high milage engine has "sludge"built up and sometimes that "sludge" is keeping it from leaking. When you put full synthetic into a high milage engine that has always used conventional oil you will have leaks. It isnt that synthetic actually damages the seals.
Your example is for an engine that has not had its oil (dino or syn) changed reularly. IMO, An original owner of a car that uses ANY API Detergent Oil, will keep that enginge clean WITHOUT Any "sludge" build up regardless of the amount of mileage one has on their engine, providing that the oil & filter were chagned at regular intervals(preferably around 3000 miles). I am NOT disputing that Synthetic Oils are better for ones engine. I am just saying that if you change your dino oil and filter regularly, you will probably never see any sludge build up on that engine. If it leaks with syn, it will leak with dino(except your engine with "crud" additives or maybe those "hi mileage" oils that are said to swell the seals).