I had mentioned on another thread that my antenna would only power up about 8". So today since it was still on my mind I thought I would try and fix it. Thinking it was just a simple over run switch not working correctly I stripped out the antenna and opened it up. There are no switches as such, there is however a small circuit board which I assume controls the length of time the motor runs, and a simple slip type clutch mechanism that stops the gear teeth from shredding when the motor over runs in either direction. All this was well caked in a solid mess of dirt and grease. I disassembled the gear mechanism which leaves a tangled length of geared nylon drive shaft.

I thought I would be able to pull the mast up by hand since the gearing had been removed, but it refused to go beyond the original 8". At this point I wasn't sure if the mast had been replaced with a smaller one, but on careful inspection I could see the beveled edges of the two other shafts so after liberal dousing in WD40 at both ends the mast finally broke free after about 40mins of literally forcing it up and down. It was seized solid. after cleaning it as best I could and wiping down the drive shaft as I went I got it to run freely.

After cleaning the whole of the mechanism, re greasing and reassembly (I had to use silicon bike chain lube since it was all I had, will strip it down again in a week re clean and re grease with something better). It now works a charm.
The two bottom screws on the antenna assembly had corroded because the drain hole in the bottom was also blocked.
So if anyone has an antenna that is either stuck up or down(but you can hear the motor run), or won't motor up or down the whole way. This probably whats wrong.
Hope this is of some help to you all

Steve