If the car was advertised with a 6 stacker, then the dealer has to provide you with the advertised unit - they don't get a choice. If it's only in the specs in the manual that it says its a 6 stacker then I doubt you will be able to get anywhere with the dealer. If you still have a copy of the ad (if there was one) check it and if it's in there, you can go back and the dealer will have to fix it. You can track down the previous owner and find out if they changed it over. Even if they did, if the ad said it was a 6 stacker, they have to fit one. Hope you can solve the mystery. Good luck.