Buy at the Mercedes dealer / car but not stapled as described

I bought a second-hand Mercedes (S204) in 2012 from an official Mercedes dealer. It was advertised as “checkheftgepflegtgepflegt”. Now it happened at a workshop meeting that only three of the actual six inspections were carried out in the digital checkbook. Thus, it is not checkedheftgepflegtgepflegt. I told the dealer this lack of material and pointed out that he did not comply with the agreed quality. In addition, I have informed him that my statutory warranty rights (re-fulfilment, withdrawal, reduction, damages) now apply. Since one cannot catch up with the missing inspections and I do not want to return the vehicle, I have proposed to the dealer a reduction of the purchase price. He has rejected this with the indication that in the purchase contract nothing is taken care of. Does anyone know about this? What is the legal situation? Do I have a Chanc to demand / get a reduction in the purchase price ?