Remove the plastic from the inside of the hatch. That allows you to access the spoiler nuts/screws and detach the spoiler plate. Reseal with "Mortite" weatherstrip and caulking cord.
You can check the wiring rubber loom at the top of the hatch both side to be certain it is setting properly and without tears.
There is also the possibility that the rubber around the door you open for filling the gas that could leak. If it fits tight; You are good