Originally Posted by userfriendly
I use group II mono-grades to clean up the gunk synthetics leave behind and to un-stick and clean up the rings and pistons.
Works for me. I heard about the GPII thing some where.
Originally Posted by Sayjac
I think the best explanation of the reason "some people" like EricTheCarGuy might say it was in his conventional vs synthetic youtubes, specifically that part that deals with leaks. He took a lot of heat for his initial yt on conventional vs synthetic oil, so much so he did a follow up. I would say it most applies to much older engines that have run conventional almost exclusively. Synthetic oil doing more cleaning may tend to expose some areas not kept as clean by conventional, and thus leaks become more prominent.
That is like the pictures the syn oil pushers use to prove "conventional" oil make sludged up engine. Those engines are engines they are not properly maintained.