Our mechanic looked online and said this seems to be a not-so-uncommon issue with the Ford Explorers. Saw another person on this website who had a 2007 Explorer with this same issue back in 2010. It seems to be a design defect and something Ford should fix but that will probably not happen. Just glad I had the cash to pay for it and another vehicle to drive during the week I was without my car. Still, it is painful to fork over almost $1000 for something that should have been Ford's issue.