We recently encountered our driver's seat stuck in the fully rearward position.  When attempting to move when we pulled up on the handle the seat would come forward less than 1/2 an inch.  The locking pins were engaging on both sides and would correctly lock the seat into position.  After a couple of attempts to determine the cause, I was finally able to identify the culprit.  It was a nickel that was lodged in the outboard track at the very back of the seat track.  It was just sitting there in a slot in the track and whenever you attempted to move the seat it ran up onto the nickel and stopped it cold.  To fix it, I was able to push the nickel up with a very small screwdriver and then move the seat forward where I could fish out the nickel out with a couple of small screwdrivers.  Lift up on the nickel and get the bottom to move out of the track and it will fall out onto the floor.  Hope I can save someone some time and energy or maybe some service $.  Could have been an expensive nickel.