If it is an 1981 Farimont, it is likely that the seals are already leaking. I
think the idea that synthetic oil can casue problems with seals and gasket is
overblown. However, if you are really worried Mobil now has a "high mileage"
formula syntehtic blend oil that claims to condition seals to reduce leakage.
http://www.bestsyntheticoil.com/amsoil/seals.shtml - I know Amsoil, but they
can't always be wrong
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