Car Parking allotment

Dear Sir\Madam, Am interested in one flat in a prominent society in Bangalore. That flat was taken possession recently Sep 2015 and the seller (current Owner) have not registered the flat yet. So I will have to go through the assignment process to get the flat assigned to me by the builder. So the Seller have paid the appropriate assignment transfer fees and also submitted all required documents. Builder is stating that they will do the assignment process, but documents issued already like Possession letter & car parking letter would still be in the name of Seller. My concern is if they DO not re-issue the car parking letter in the name of buyer, then what would be my hold on the car parking slot. Builder also insists that they will not mention the car parking slot number in the (to-be registered) Sale deed, builder says that they will just mention that "One covered car parking in the basement" but not any car parking number. This would mean that I have to always have the car parking allotment letter issued to Seller. In addition we were not sure how the car parks were allotted to the owners, for example the car parking slot for the flat am going to purchase is in Basement 2 with no left and direct stair case access. These are my issues. How do I approach these issues legally? Any help is appreciated. regards, Arun