Spydernut

I'm pretty sure someone hijacked just the driver-side mirror on my 2010 Impala LT. I found no broken glass, nor dings to the mirror housing. I ordered a replacement glass (non-heated) with the plastic backing. But for the life of me, it wont fit! It seems the circle on the back of the new mirror is just a hair too big in diameter and possibly not deep enough to latch on inside the rubber boots around the motor. Also, the metal latch/bracket on the outer corner really doesn't "clip on" to the plastic arm. Please tell me there isn't a piece/bracket broken on the mirror motor. I'm afraid of taking off the RH side just to see how it attaches. Shown below are the pictures: