I have access to the inside and I unscrewed the antenna itself. There's a tall plastic bracket that snaps in place at the base. Towards the top, what looks to be a brass antenna base that looks attached to the tall plastic bracket. At the top are two arrow pointed spires. I don't see where anything twists or rotates without warping the fender.

Is the removal from the outside somewhere? Here are some pics.

 

grab the piece with the 4 slots in it with pliers and spin it off.. you may have to use PB blaster or wrap the pliers with electrical tape if you dont want the black piece to get marred up

 

Thankyou