I used the lemon law here in NJ, on a 93 corvette which also had a water leaked after numerious attemps to repair(8 attemps ), Even had the "water doctor" tried . every time it rained or washed the car the interior was wet. You have to give the dealer 3 attemps to repair , then you can file the paper work(dealer suggested I start proceedings). After about 6/7 months I received a check for the car and any interest I paid on the note . The lawyers get paid by the MFG.
PS your command of english is outstanding
You bought an SSR, and got an interior shower at no extra charge? :lol
The water leak is most likely the matter of either weatherstrips not seating/sealing properly or the window adjustments. Without testing it myself I couldn't tell you exactly what the problem is, only a few possible things to look for.
FWIW your going to have to jump thru a few hoops ,but you should be able to get the settlement you want. Just have the paper work , copy everything and if required to send anything to the mfg, follow your lawyers information to the Tee.Get the required lemon law paper work & Give the dealer all the information he needs as he can help provide GM with their requirements for settlement.