First off, almost all the so-called "synthetic" oil being sold now is NOT synthetic. It's plain ol' ordinary dinosaur oil that the oil companies have played Van Halen at high volume until it submits. Lots of what is sold as "synthetic" in the USA (Group III) cannot be sold as "synthetic" in Europe, where the courts have not allowed the oil companies to mislead their customers.I’ve never seen any evidence that synthetics ever CAUSE leaks. It’s usually a far superior oil anyway. I really like redline.
www.motor.com/2022/03/are-all-oil-groups-the-same-oil-differences-101-for-service-and-parts-professionals/
Are All Oil Groups the Same? ‘Oil Differences 101’ for Service and Parts Professionals | MOTOR
When performing oil changes, technicians typically reference and adhere to vehicle manufacturer specifications.
www.motor.com
Thousands of years ago, when oil sold as "synthetic" actually was synthetic/Group IV, (primarily Amsoil, but some other niche companies also) the synthetic oil would dissolve carbon deposits and varnish near the seals and gaskets; when these "false seals" went away, the ancient rubber, cork, and rope seals would start leaking. MAYBE there was some interaction with the actual synthetic oil, and/or the additive package that caused leakage past old seals...but that's beyond my pay grade.
Short story: No real reason to be scared of "synthetic" oil, 'cause most of it is falsely-advertised dinosaur oil that's been refined 'n' processed. The genuine synthetic oil is no enemy of gaskets and seals in good condition. MAYBE genuine synthetic oil leaks faster from damaged/worn-out seals and gaskets, maybe not. The better plan is to fix the crappy seals and gaskets, and use a top-grade oil
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