Quote Originally Posted by ontarian_frog View Post
You'll be fine. I have yet to see proof that synthetic oils cause seals and gaskets to leak. They would sweat a little but not leak, and that's for engines with A LOT of miles on it.
I'm guessing someone tossed some synthetic in their 100 year old model t and a gasket went out :P

This probably got started due to materials used in older cars... so "I switched to synthetic at 250k miles and the main seal in my 1965 mustang started leaking" ... Older/different materials with a high age might react funny to the detergents, but I doubt any modern (1980+) car is going to have an issue