I have a similar prob with my '07 Mercury Mountaineer Premier. Last November, the left powered 3rd row seat back wouldn't fold down. Dealer said it needed a new motor, so he ordered one. The warranty covered the cost, plus a loaner car. A hassle, but I assumed that would be the end of it. Little did I know ......
Fast forward to last week. Same problem with the right side seat. Seat back locked in the up position. The motor will wiggle the seat back and forth, but it will only move a couple of inches before it stops. Seems to me like the motor is okay but the mechanical mechanism (maybe gears?) of the seat is locked in position. I can push on the seat back and move it a little, but am reluctant to try too hard for fear something important will break and it would then be my fault.
Original warranty is now expired, of course, but at least we have the ESP Premium FoMoCo extended warranty so, if needed, that will pay for the repair less a $100 deductible.
Regardless, it's disappointing that we have have had two problems with these power folding seats. Although the truck is over three years old, we probably have not used the 3rd row seats more than half-a-dozen times since we bought the truck, so the vast majority of the time they have stayed in the folded-down position. Any way you look at it, that's terrible reliability.
Must say, however, that other than this problem, this SUV has served us extremely well. It's my wife's car and she absolutely loves it. I like it too, but I'd like it a lot more if this recurring seat problem could be solved for good.