Problems with Mercedes Oltimer sales

Last weekend I sold my Mercedes 190 SL privately, which I have already sold for more than 20 years. I actually only drove with it in the first 1-2 years otherwise it had actually only kept it as a valuable investment. On the day before, I wrote that the vehicle has been standing for almost 20 years and is therefore not ready to drive. Extensive work is therefore necessary. Now the buyer called me and accused me of having sold him an accident car! r said that I can’t take over the accident-free warranty because the car is from fourth hand. I could only do this if I were the first owner of the car. Originally he wanted to bring a professional at the first inspection, but refused this because I didn’t want to show the surroundings to every stranger. The car is standing at my uncle’s in an air-conditioned hall with valuable helicopters and gliders (models). In the contract was also under exclusion of any warranty. I am not aware of an accident and certainly not in my time. The car always ran well ! He said the frame was completely spoiled. May now be only a used car of private sale if I have examined it before for an accident expertly. So it still comes ! I suspect that the works (rust etc.) were too extensive for him that he is only looking for or found a reason for possibly. I don’t have to give any guarantees as a private person, or ????? After that, he only expanded what about the car (valuable spare part etc.) and wants to give it back to me again train by train. He already has the car in his possession for 5 days. But does not want to rewind the contract. The freight forwarder at the same time his technician had the opportunity to take the car into consideration at the second date (before payment).