TV Aerial Mast Difficult to Move

I’m after a bit of advice regarding the Vision Plus Status 560 antenna on my caravan please.

The mast is very difficult to move up and down through the mounting sleeve, and the locking collar (which is up near the top of the mounting sleeve) is difficult to turn in either direction.

I can't find any information on whether there is any maintenance that should have been done, or lubricant that should be applied.

Has anyone had and fixed similar problems? 

Many thanks.