I bet this is the issue....

the gears break teeth and fail to work.

the one you need to replace it the easiest to repair. it is right behind left side of the glove box. you can remove the glove box and see if the motor has a good connection or is just spinning and not changing the air direction. this is the same motor as the hot/ cold temp door and the fresh or recycle door and the same unit in the back air handler. goto a junk yard and get a replacement. if the issue is fixed eather get a new part or leave that one in untill it dies. i got one year out of the last one i swapped....mike