I have a 1991 Legend L with 71000 miles. is it too late to use Mobil One oil(syn)? i know that in muscle cars if you start using Syn oils after 40000 miles, they start leaking. that is due to the Sync oil cleaning removing build up from the system. Sometimes the Sync oil remove tiny particles of old gaskets and that is why engines start leaking. like i said, for American Muscle cars thatis what happens after 40k miles or so. does anyone know if the same applies to the legends? thank you.