driver's side seat frame or railing continues to malfunction

Extended warranty covered the first repair, but would only give us a used part from a vehicle that was in an accident. They claimed the seat was not damaged. How would we really know!! The Toyota dealership didn't want to install the part and recommended a new frame, but the warranty refused. The only reason we agreed to it was because the claimed that the air bags could affected because a plastic piece was broken. Now the seat makes a lot of noise and whatever is going on, can be felt. The warranty for the work expired this past July and of course they won't help us. The existing extended warranty does not cover this issue and it's going to cost $4300 for a new seat. This just sees like a manufacturing issue with the seat frame/railing for this vehicle. The extended warranty should not allow inferior used parts for seats with air bags. Where is the compassion for dedicated Toyota buyers safety? I've purchase 6 Toyota vehicles over the years. I'm done!!!