Those elect. motors seize up if not covered in winter rains/ moisture. It's the bearing in the lower end of the motor that goes bad and that's usually before the jack mechanism portion shows problems. So I cover mine with plastic and wrap each one every winter.
You should run each one up and down every so often too. Don't let them sit idle for lengthy periods.
By running each one up and down individually you can tell by the sound if one is developing a problem as it will be a louder grind less smooth sound than the others.