I went to my Ford dealer last week, to have a new key made for my remote start. While I was waiting, i asked the service manager if there was anything I could try to get my locks to work again. Their is not a lock on my ST that works anymore. Both the front doors, the tailgate, and both locks on the cover are froze up. The service manager had me pull into the shop, and he used penetrating oil and worked the lock by shoving the key in and wiggling it around then pulling it out and repeating. He got both front doors and one of the bed cover locks to work again by doing that. I was very happy, and he didn't even charge me for his help! I am planning to work on the other two locks, to see if I can get them working again. He told me that it was a fairly common problem on Sport Tracs. Hope this helps.
Brett