Ive persoanlly seen synthetic start leaking when it was put in a conv oil engine. You can definitely tell syn 5w is much much thinner than conv oil.

I run Castrol conv oil. If you do the math, a engine rebuild is like 300 bucks on a 20 or 22r. Changing the oil 50 times, when its 10-20 more a gallon equates to 500-1000 more bucks that your throwing at your engine through its life. Some ppl close to 2k more. Some people love the peace of mind from having a tad cleaner oil though.

How many people have actually seen oil related engine failures, when oil levels were properly maintained?? Regardless of the brand or syn vs conv? Yes conv does gum stuff up more, but if you change it at the right times, its very moot point to argue.

Oil is Oil IMO. Change it every 3-5k, or 10k if your run syn and wanna push oil that long. Everyone is gonna ahve their opinion, and its very unlikely your gonna change someone elses. In the car world, oil vs oil, is live chev vs ford