Used car purchased, probably ZKD broken

Hello guys, I got a Golf 4 with 125tkm from a dealer this week. He tried to completely exclude the warranty from the contract. Shouldn’t be possible by law. Now I have the following problem: When I picked up the car, I noticed at home after I turned it off that he lost coolant and hissed it in the engine room. I drove to my workshop the next day after consultation with the dealer. Now the call from the factory stat t – In the cooling water sealant was found and it could be that the cylinder head seal is over, i.e., the deficiency was already known before and was kept secret. What can I do now? Because to know exactly what is now thing the suction bridge etc. must be removed now, which is naturally associated with high costs. Thanks in advance for your help