Audi A6 C7 3.0 Stronic Problems

[C20SYJ]

I have noticed for the past 4 months an oil smell when sitting in traffic in D with my foot on the brake however if i shift it into N it seems to stop. It happened maybe once every 2 weeks. I've had it at my normal mechanic and an audi specialist and neither could find any problem or leaks and the oil levels are all perfect. As off 2 weeks ago I've noticed it more often however the car also shuttered for about 2 seconds when taking off from a stand still and there was a kind if rattling noise. Its fine it a couple of times since. I've had it back out at my mechanic and again everything is fine and no signs of a leak. He even plugged the gearbox in with no fault codes showing. The only thing he can think off is the clutches going in the gearbox but that's only an educated guess at this point. Does anyone have any idea before I take it to the audi specialist and he bends me over.