My '08 X5 mirror sticks in the tilted down position, usually after going full tilt after backing up. I can un-stick it by pressing on the mirror and simultaneously working the switch. Change the mirror selector switch so it doesn't automatically tilt down while backing up. There is a DIY on disassembling the mirror and lubing the mechanism. This might solve the sticking problem.

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'21 X5, '15 435i, '10 535i, '08 X5, '98 M3/4