I have an 06 M3, so I'm not positive if it is the same, but I'll tell you what I know. I had my windows tinted by my sister's boyfriend - he's really fussy and took everything off that he could to get a good tint result. Anyway, the third brake light cover should just pull straight down - there are two plastic pieces that pop out. When you get the cover pulled off, there are two black plastic tabs on the LED panel that slide outwards (toward the sides of the car). This will release the LED panel. Then, there is just a plastic plug-in connector for the wires.
To take off the rear deck, you must:
remove the headrests (pull straight up)
unbolt the child seat anchors (plastic covers lift straight up to reveal bolts)
tilt down the seats to take out several plastic plugs (not sure if you don't have folding rear seats)
pop off the speaker covers (these lift straght up)
unscrew the rear deck speakers (3 screws each)
unplug the rear deck speakers
unscrew the subwoofers (from underneath inside the trunk)(4 screws I think)
unplug the subwoofers
lift out rear deck
I think that was it - there was another plastic piece way back along the bottom of the window that was held in by 3 or 4 screws (which are exposed when the rear deck is lifted off).
Sorry that the details are a bit fuzzy and no pictures were provided - it was a while back. All I can say is that if you are patient and look before yanking stuff off, it is certainly a job any of us can handle. I may have forgotten a screw or plastic plug somewhere - perhaps other members can add/edit the list of procedures.
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