MBSA unable to fix problems

I took possession of an approved used Mercedes-Benz E350 Cabriolet on 5 August 2015 at a cost of R 490 000.00. The car was supposed to have been serviced before delivery but upon receipt of the car it was obvious that no inspection of the vehicle was done prior to delivery as the navigation system did not work at all. I reported it to the salesman who assured me that the problem will be fixed after the weekend. From the symptoms it was obvious that the navigation unit was faulty but a software restore was done with no effect. The antennae was then identified as the problem and after replacing and respraying it, the problem still persisted. After 3 weeks I am now told that they need to try another couple of solutions as it is too expensive to replace the unit. They cannot give a time but it could be a couple of days or even weeks.<br> If the car was properly serviced in the first place this would not have happened and it is a very poor reflection on MB that such a unit is not replaced immediately on a relatively expensive car. Is it MB Century City who are clueless or does MB not guarantee it's products properly.