Front seat jerks into position

I have a 1999 Lincoln Continental. The front seat jerks as though it’s on a cog railroad track when I try to move it forward or backward. I had to turn off the entry feature where the seat automatically moves back and forth when you put the key into the ignition. There is no foreign object in the track and it is clear. The only opinion I’ve received is from a local mechanic that said he would have to replace the entire mechanism under the seat because he can’t get just the motor that moves the seat, at a price of almost $700. Does anyone have any other ideas? Thanks.

It’s more likely to be the gears than the motor anyway. You may be able to find the assembly cheaper at a junk yard.