A couple months ago I replaced a broken antenna mast on my '97 850. It started out working great and now it'll sometimes retract all the way when the car is off and other times it'll only retract about 2/3 of the way.

It seems to go in phases - works great for a day or two, doesn't retract all the way for a day or two.

What could this be caused by?

 

Damn things are a pain in the butt. Mine do the same thing and I have replaced them multiple times. I have tried lubing them, but that does not seem to do much good either.

 

The quickest and simplest attempt to fix this is do what the owners manual suggests. Spray it with WD-40, wipe it down then do it again four or five times. Mine did what yours did and so I followed their advice and actually did that around 5 times. Guess what? It worked. They recommend you do that around once a month.