1999 Lincoln Continental driver seat track assembly

After over a year of the driver's side seat******** back and forth when moved, it now won't move at all. I only get clicks when I press the button forward. The seat does move if someone gets in the back seat and pushes with their feet while I push the button, but hardly a reasonable solution. The car has two drivers, one with long legs and one with short legs, so just leaving the seat in one position isn't an option.
Is there a problem with choosing a used driver's seat track assembly over a new one? Is this such a common problem with this car that there's a good chance I'll have the same problem with the used one and have to replace it again?
I've gotten several quotes from repair shops and they have all quoted me replacement and labor costs of around $1,000. I asked my main shop to look into a used one but haven't heard back from him... I think he's stalling. I've researched it myself online and found several available, all with a 30 day guarantee. I'm just worried I'm being penny wise and pound foolish in opting for a used one, even though it's at least $400 cheaper. Thanks for any info you can give me.
I have a 1999 Lincoln Continental, 8 cylinders, 123,000 miles