The part that is supposed to break; they call it the ball stem. It's the plastic part between the arm and the head. The ball is also the bottom of the backing plate that holds all the motors, elements, etc. That in itself is a poor design. A part designed to break to protect the mirror components and the vehicle door should be a reasonably simple part to replace. They designed this mirror unit to die a $450 death when impacted for a part that could easily be designed to cost $5.00.
Call them, try to buy a ball stem.
I've got a brand new mirror still in the bubble wrap if anyone believes they can use it. I'm going to put it on EBay for a couple hundred bucks and see what happens. I thought about repairing it myself with a simple bolted fix but I DO want it to break where it did; better that than it be solid and twist the door frame.