It's not air flow to the motor guys, as a matter of fact it has nothing to do with the motor or the oil inside the resevoir. It is all about aerodynamics, behind the drivers seat there is a oil cooler box. This box has a enclosed radiator type grill system that pulls air from under the car to cool the oil in the resevoir mounted in the box.Unbolting the oil cooler lid relieves the pressure under the car, venting trapped air from under the car into the trunk or cockpit where it can escape. I'm sure everyone has held their hand outside the car while driving down the interstate, when you hold your hand straight out, cupping it causes the air flow to push your hand backwards, while holding it flat like a airplanes wing, reduces the drag. Having the lid secured causes restricted air flow, acting like a parachute. Huge advantage for the #99!