Ill go with myth on this one.
Synthetic oil dries out seals.
- Thread starter AZjeff
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The myth LOL just like water will dry out your lawn!
I prefer my seals clubbed. 
275k on 2010 civic all Mobil 1. Have actually been thinking about using HM oil on it. But, don't want to fix something that isn't broken. This car doesn't burn a drop of oil. Changed every 7500 miles myself. Never been to a shop for oil changes. Best car I have ever owned. Goal is 400k.
The key is to change the oil frequently. Oil has seal conditioners in the oil. One that never changes there oil will eventually end up with oil leaks
Thank you George Carlin
My favorite comedian. RIP
It's true though. I've almost given up on responding to oil questions on other forums and social media because nobody listens most of the time. They'd rather cling to the myth. The saying "smart people sound like stupid people to stupid people" tends to hold water in those discussions. If you come across as more knowledgeable on the subject, especially if there's terminology they don't know, they'll perform whatever mental gymnastics necessary to skew you as the stupid one. People don't want to be factual, they just want to be right, and will go to great lengths to make that so.
Aren’t most seals Silicone based instead of rubber nowadays?
For newer engines, I'm not really sure. I know the GM LS based engines used a teflon infused rear main seal which was about the dumbest thing they've ever done as no seal conditioner will touch teflon. It's why they are notorious for rear main seal leaks.
I believe this comes from early synthetics getting past old rope type crankshaft seals. Which did indeed happen. It wasn’t the fault of the oil of course!
I had just the opposite experience. I took some shop classes in college so I could have access to the garage and the tools. I learned a ton because the professors would leave their shops which were functioning, commercial entities, come to the college, teach a couple of classes, and then go back to the shops. It’s hard to live in a bubble of ignorance when you have to live in the real world and meet payroll, deadlines, troubleshoot, and eliminate callbacks. I wish all “higher” education was like that. We certainly could use that now.
Wow! Sounds like that instructor owns a shop and is teaching sales instead of auto repair! Gotta keep customers buying the top-dollar lube jobs, because you never want them to buy the cheap conventional lube...
Really gave me a good laugh!! I use to haul petroleum products from several western NYS and Pa refineries. One of the the products was a undercoating product that we hauled up to Ontario Canada. It was said that this could also be used as baby oil!
Shaft seals, as well as end plugs can be fluropolymer(FKM, Teflon) or neoprene/nitrile. RTV FIPG is for static face to face joints.
Wait does that mean if I use synthetic and then never change it it will turn into coal (burnt sludge) and then dry into diamonds? Does that mean I'll get diamond plated camshafts that don't need oil?
I guess I'll stop changing my oil and get some synthetic diamond coated bearings
Oh wow 
I should stop using synthetic oil immediately
I should stop using synthetic oil immediatelyRedline is a synthetic oil and definitely won't dry out the seals.
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- Mar 14, 2023
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This info started with the very early formulations, it did have a tendency to cause seals to shrink not having conditioners combined with old rubber formulations. Not so much a “myth” but no longer applicable.
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One thing that makes it even more irrelevant is the chemical composition of modern base stocks. For the most part they are not majority Group IV (save some of the boutiques) and therefore they are chemically similar to a conventional. As noted above it was the PAO that was the problem.
