Only after driving long distances the bottom of the vehicle is covered in oil

This car has a strange problem. When city driving, daily routines, and small trips, this car will not lose a drop of oil between oil changes. But, when driven on a 700 mile + trip, the entire bottom half of the car becomes soaked in about two quarts of oil (still a little bit on the stick after round trip). I can't see anything actively leaking, the pan gasket is dry and eventually all of this oil will cook off and it'll seem spotless again. I'm really racking my brain about it.