You are correct. I removed the cushion and the water comes in the trunk from there. The question is why the water gets blocked underneath the torx bolts. Even If somehow we seal the two pieces then, I could assume that the water will still be blocked somewhere else in a different area of the car. How we can make sure the water will go down to the floor.
realistically if you want to fix it permanently its going to require you to completely remove the plastic box and clean out the entire area underneath and then use a silicione gasket material and maybe some rubberlines to completely block it. It would seem to be a engineering defect from maserati that wasnt intended or they just didnt care to fix lol as body of the car is basically the same from 2007-2018 so the issue theoretically should affect any car that sees significant rain.I would not recommend putting the cushion back in that spot as its going to just get moldy and cover the water.
Since the MC version has a different exhaust layout that comes out the middle of the rear bumper I wonder if the trunk box is shaped alittle different which would also make the water drainage different, but knowing how they made this car with super cheap materials in some places im guessing they made as little changes to the models as possible for cos.
. I just double check my trunk every time theres been a major rain for a week or so just to make sure nothing is wet in there as my trunk is usually empty anyway so it only takes 5 seconds to pull off the carpet top and smuggler box and inspect and clean with a towel.