Synthetic oil does flow more readily than petroleum oil does so if you have a leak it will tend to leak from it more freely. This however is caused by an all ready failing seal. Not by the synthetic oil itself.

Petroleum motor oils are notorious for forming what's know as a "false seal" Varnish and crud will build up around a failing seal and help keep a more viscous petroleum oil from leaking. Synthetic oils that are highly detergent will clean off the build up and expose the all ready failing seal. There's your leak!

For this reason we suggest that our oil's only be used in mechanically sound engines. If you have a leaking seal replace it prior to installing Amsoil motor oil.

We have also seen many cases where older engines are starting to seep oil because some motor oils have poor long term seal compatibility. Exposure to these low grade oils causes the seals to harden and seal poorly.

All motor oil, synthetic and petroleum alike contain chemicals as part of the additives that are added to the oil that are there to keep engine seals pliable and to cause mild swelling so the seal works properly.

The additive's in Amsoil motor oils are so good at conditioning engine seals that there have been many cases where engines with slight oil seeps sealed back up after a few thousand miles of driving. That being said if the seal is shot all you can do is get it fixed, no oil will fix it ours included.