mc,
I remember reading a tech article in Road & Track a few years ago that said full synthetic oils are missing certain natural components that aid in keeping some kinds of oil seals in good condition. Because of that, the seals might deteriorate and lead to leaks.
That article was from about the time Mobil 1 hit the market. Since several years have passed, it's possible that oil companies have changed their formluations to avoid that problem. It's also possible that the auto industry has adopted newer materials that don't suffer when full synth oils are used. I know Porsche uses Mobil 1 as OE oil as does Chevy on the Vette.
I thought it might be worth mentioning.
