I was recently rear-ended in my 97 F150 4x4. The dealer replaced the frame bumper to bumper. The driver seat track was damaged from the impact. The dealer replaced it but, the replacement track is shorter than the original. The original is 27 slot, the replacement 24 slot.
Can you see the problem? The dealer did not recognize after insalling,(or before installing the replacement track) that the driver seat is now closer to the steering wheel,(nearly 3 inches) when the seat is set at it's furthest back position.
So, when the 40/60 split seats are positioned furthest back, the drivers side is nearly 3 inches closer to the dash than the passengers. The dealer wants to remedy the situation by replacing the passenger seat track with the shorter version. There goes the legroom up front.
Apparently, the manufacturer quit making the 27 slot seat track for safety reasons I was told. "This was done in late 97 models," said the dealer. To make it worse, there are no 27 slot tracks on the parts department shelves, nor at the manufacturer.
I just as well would like my old 27 slot seat track back even if the seat slips a slot once in a while. But no! The dealer tossed the original no sooner than they could install the replacement 24 slot track.
As an inconvenience, either the third person up front in the middle gets an uneven seat, or the passenger side move forward losing leg room.
Please, before you have your seat tracks replaced because of unwanted slippage check yourself to see that the replacement track matches the original. Because the dealer will not do such nor care.

 

I would check the bone-yard. I've been to a few accidents with the '97 and newer F-150's. As many as they have sold there has to be some retired somewhere.