The National Highway Traffic Safety Administration (NHTSA) is upgrading an investigation into complaints of severe corrosion in the rear wheel wells of certain 2004 Ford Freestar and 2004 Mercury Monterey minivans. The anchor plate for the rear seats on these minivans is mounted on the rear wheel well and difficulty latching the seats is being blamed on the corrosion. There have also been complaints of the anchor mounts detaching from the vehicle completely. The upgraded investigation will include 2005-2007 Freestar and Monterey vans bought and registered in both salt belt and non salt belt states. If the investigation should lead to a recall, almost 83,000 vehicles could be affected.