Sticky Antenna

I've just bought my first BMW 2 weeks ago. It is a 1991 318i. I don't know alot about the model but from what it looks like , it is pretty well loaded. I have ordered the Robert Bentley service manual and its on its way. I need to know how to take the automatic antenna apart because it gets stuck 3/4 of the way up and on its way down it gets stuck at 1/4. I would just start taking things apart but i am worried that with it being automatic, it may be very tricky to put it back together again if i take it apart in my own monkey wrench banging way. Any suggestions would be very helpful.

Thnx