What happens is inside the aerial unit, the grease hardens over time with water getting into it I guess....
This grease then turns into a soapy state thus not allowing the internal components to freely move. It then gets to a point where
stress is placed on the weakest component. This being the mast with the teeth on it. The mast snaps in one or several places thus
reducing the length of the antenna. With a simple push down it will grip onto the cog again.
Anyhow, point is when you have a working antenna, take it off and see the state of the grease inside the unit. Clean and replace the
grease to preserve the mast and hopefully you won't require a replacement mast from Autobahn at a ludricrus price or even the wreckers. I've had to replace my mast already. I do have one that still works from the wreck that I am still selling. Make a reasonable offer for it. I will be selling the whole unit reconditioned with new grease inside it.