exhast and dirt and dust entering vehicle through back door

dirt dust and exhaust fumes entering the car dealer said common problem on 2010 through 2014 tarrus. they have what they call a dust kit to fix the problem for 1250 dollars plus labor how ever by the time i figured out i had a problem it was 3000 miles over warrenty i bought the car with 32000 miles on it during the winter so i did not notice the problem till may and by then the car had 39000 miles on it so the dealer nor ford would help