WW bought with hidden water damage

Hello dear WW friends, I have a problem and think you could help me on the jumps: I bought a WW in summer (Bj 1993, from the dealer who made me notice a “resolved water damage” in the area of the door). So it is also in the contract. When my children (I am already Grandpa) wanted to use the part in the autumn vacation and we made it float, we noticed in several places, especially rear side and rear side surfaces and the connection between floor plate and side walls and rear wall that the car was there, well, marode. I had called the dealer in September and we agreed an appointment for the inspection and arrangement. That was today and now he told me the following: 1. Water damage is normal with old WW (1993) 2. the damage he would not have been able to get away from the side of the picture wall (although he had a few centimetres beside the said places often after the TÜV, I had not seen the “right” water damage from Kulanz. Well my question can not get away from the side?