Does anyone know how to get the plastic cover of the stem on the rearview mirror?

The mirror is loose between the base and whatever connects it to the window. I am afraid of braking the plastic cover. What's the trick?

Thanks for your help!

What I woud do.. is maybe try to get a heat gun and heat up the base a bit, hopefully that will melt the sticky stuff and hold it tight for 1 min..

How can I get the plastic cover off the neck and base. It seems to be in two pieces. I cannot figure out how to get it off without forcing it.

Any idea?