AudiForums.com - Auto dimming rear view mirror question

Car: A6 2000 2.7T

Hi all,
My car is fitted with the automatic dimming rear view mirror; however I am not sure that it is working properly. The garage where I bought the car from was meant to replace it as part of the deal. But I think what they did was buy a new glass, open up the casing and put it in. My mirror currently has a kind of brown tinge to it during the day and at night the headlights do no seem as bright as they would on a normal mirror but not as dim as a standard mirror on night setting.
So here are my questions:

How do I tell for certain that my mirror is working properly?[/ol]

What should it look like on the night and day setting if it is working correctly?[/ol]

If I need to replace the mirror can I buy one from a later car with the compass in it and install it without any problems.[/ol]
Thanks in advance.
James