If at any time you get errors related to EVAP (small leaks, etc), chances are your gas cap is not holding pressure in the tank.
This is one of most common ways to fail inspections. Then they sell you a gas cap at twice the price, charge you for half hour or an hour of time, and you end up paying $250 or more to get it done.
Who on here finds this a familiar situation? Don't raise your hands (I wont see anyways...lol).
Well, you can get this done in about 5 minutes, if you include a break (should you get tired during the install).
Hope this helps others in their quest to be a DYI master on Panameras.
I think I got part from eBay - genuine Porsche Panamera gas cap - ~$35 shipped.