I have experience with synthetic motor oils for gasoline engines dating back to the '70s, I have seen the insides of dozens of motors fed a diet of synthetic motor oil. That's why I have run them in all my personal vehicles, and recommended them to freinds, family & customers since the '80s.
The most compelling reason I choose to run the synthetic oil is that there is no coke build up in the piston ring grooves, but the fact that it is hard to find wear anywhere in the motor is an added bonus. I certainly wouldn't spend the extra money on synthetic oil if there were no tangible benefit. I have never seen rust, but I can't recall if any motor could be described as having sat for long periods of none use.
Your friend on the DTBB
my last post on the subject
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