The front passenger side power bucket seat won't forward or back in my 2006 Navigator, it moves up and down, but that is it? Any ideas?

 

Stripped gears are common. There are 3 motors under there, which leads me to think one of them is not with you anymore.

 

When I first got my new to me 2005 Navigator the driver side seat was jammed in the far most rear position. I removed the cover and manually spun the motor/drive assembly a few dozen times. Then I turned on the key, forget if it has power key off, hit the button and then it worked like a charm for the next 14 months before I traded it.

Once I got my new to me 2006 Navigator the passenger side side seat jammed in the same far most rear position. Did the same trick, never has acted up again in the last 2 years.