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Can you provide the last 7 digits of the VIN of the vehicle, so I can provide better assistance?
Hi, do you still need assistance? Or the order cancelled?
This issue typically stems from the mirror electronics module failing. Since both mirrors are acting up, you will likely need to replace both modules, although since the drivers side is the master and the passenger side is the slave, sometimes you can get away with just replacing the drivers side module. The modules communicate on a LIN bus between each other; when one loses communication they cannot "speak" and will act erratically.
The part is number 5 in the diagram. http://www.realoem.com/bmw/enUS/showparts?id=VA33-USA-09-2006-E90-BMW-328i&diagId=51_5704
The mirror glass needs to be removed to replace this electronic component, and is very fragile. If you are not comfortable removing it (it pops off and is held in by tabs) you may want to have a repair shop take care of the repair as the mirror glass is NOT cheap and easily breakable.
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Yes, you are correct. 398 part number.