See link to my similar issue re gas fumes in the cabin. My dealer never figured out the problem after keeping the car a week but pretty much same symptoms as you except gas fumes vs burnt oil. When stopped in traffic or upon start up when warm the fumes seemed to come in through the center AC vents. Never did smell anything under the hood/bonnet. It's still happening and I'll mention your fix next time in for service.

Gas fumes in cabin
Anyone notice gas fumes intermittently coming in through ac vents? Seems to happen more when tank is half full or less. Can't smell any fumes inside engine compartment so must be coming in from somewhere else. Seems to be getting more frequent. Didn't notice this until I had put around 2,000 mi...