You just had to give me this challenge didn’t you?

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There seem to be two ways to get the unit off:
1) from underneath there is a small plastic cover which exposes three screws. I tried to loosen them but they are tight and the angle doesn’t help so I gave up. Maybe with the right screwdriver it will be possible.
2) inside the car, simply pull the “tweeter” holder off, it attaches with one plastic plug, easy removal. Then there are two bolts holding the mirror on (at least I could only see two). The problem is you will need to remove the door panel to get to them.
Have a look at the pics I just took (they seem to have loaded in reverse order):
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