[TowerTalk] Mast froze in cold temps and would not turn

[Gary Marks]

This past Winter, and as the year before, my mast froze in place when the temperatures dropped below freezing. I had previously thought that the problem was moisture getting into the rotator (Tailtwister II) and since it had been up for 25 years, I decided last Fall to rebuild it.
This past Winter it froze and would not turn again when temps dropped below freezing. The tower is a Hy-Gain HD-70.

Is there some area that requires lubricating between the mast and tower or possibly the thrust bearing although it is a bronze bearing that shouldn't need lubing.  Could water be laying somewhere and not draining. 
Any suggestions as to what the problem might be ?