general problems of the 2002 Chevrolet Venture

Several months ago, a hole appeared in the driver's seat of my year old Chevrolet Venture van. The dealership informed us that something about the way that the airbag was installed in the seat was causing problems and that they had replaced several seats in other Venture's, both for the hole and the potential safety defect in the airbag. Now, the same type of hole has appeared in the front passenger seat. The van is now 18 months old and has over 36,000 miles, so the dealer refused to be of any assistance with the problem. This is not an ordinary hole caused by wear. It was caused by a safety defect in the design of the seat which could affect the function of our side airbag, according to the dealers own remarks to us. Should not a safety defect caused by poor design be covered by the manufacturer whether the vehicle is under warranty or not?.