I've read countless times that dino oil should be used to break in a new motor, and synthetic should be avoided until around 10K. Can someone please explain the reasoning behind this to me? And if this is indeed true, why the heck are lots of manufacturers using synthetic oils in their vehicles(some with VERY expensive motors) right from the factory? I would prefer to see some evidence backing up your replies or FIRSTHAND EXPERIENCE, if possible. The old "my sister's best friend's brother's uncle's mechanic said so" kind of reply isn't what I'm looking for here.