Ted,
I'm on my second truck using nothing but M1. 230,000 on the first truck and it's still running nicely. The second has 40,000 on it. Both have had nothing but M1 since the first oil change. Neither of them leak a drop.

I've heard the stories about the oil leak thing on the truck forums. Most stories were with engines that had lots of time with mineral oil first. Could be something to it.