First, figure out what is wrong. Most antenna failures result from telescopic mast not being cleaned periodically, trapping grit and dirt between sliding sections. This puts too much stress on the plastic cord that moves the mast so the cord breaks. If you hear the antenna motor running when you turn the radio on and the mast does not move, the mast cord is most likely broken.
Another failure is the antenna motor drive belt breaking or slipping off. This is short flat rubber belt that drives the antenna mechanism. You need to take the antenna out, take the cover of and inspect the insides to see if this is the problem.
These antennas have a plastic rack-and-pinion gear drive and the gears can conceivably strip out after a long time. Again, you need to take the antenna apart to inspect these. The motor would run, but the antenna mast would not move.
Also, there is a circuit board inside the antenna that can go bad. Of course, the motor would not operate if this circuit board is bad.
You can get a new mast for your original antenna from autohausaz.com for as little as $ 14 plus shipping. I bought one of these and it works great and looks just like the original.