I've tried to do a "rebuild" on mine. Whats broke is the plastics/nylon string that pushes it up and down, you can buy a replacement string at the dealer still for about $20-$25. An entire motor will be about $125-$150. Anyway, I got mine out and tried to restring it and finally gave up and made the antenna a manual one that I can pull up and down by removing the broken string and reinstalled the broke antenna, just have to manually pull it up and down when I remove the cover.
There's usually not much I can't put back together, but this thing got me and I gave up, maybe I was just impatient that day I don't know....