I had the same with oil vanishing mysteriously, so I looked into it very thoroughly. I also noticed a lack in performance, so I start checking around. It eventually turned out to be leaking around 2 of the spark plug tubes. I tried replacing the spark plug tube seals I got from a Nissan dealership. After DESTROYING the valve cover I found out that the only way you can replace them is by replacing the entire valve cover. So the reason I never saw oil puddles was because it was dripping on the exhaust and burning off. I changed all 6 spark plugs and the valve cover and cleaned the oil out of the spark plug tubes. Holy S*** the car is lightning fast again and it doesn't misplace a drop between changes. Also another common place the VQ35 loses oil is around the oil cooler (the part that the oil filter screws onto). Its very cheap and easy to replace. Just remove the filter and there's a large nut on the same stud the filter screws onto. Unscrew this and the seal is right there. WARNING: When changing the oil cooler o-ring, you will have to drain all the oil AND COOLANT. Hope all that helps.