Need some help isolating a problem with my driver's side xenon/adaptive headlight. 05 X5 4.8is

Apparently it doesn't go up/down at initiation. The light by the switch blinks, indicating adaptive failure.

Mechanic says probably the control unit, which is kind of an expensive part. But could be the stepper motor. I didn't get the codes they read.

They suggested dropping the bumper and swapping that component left/right to see if the problem moves.

I'm hoping there is an easier way to diagnose, or maybe someone has already been down this path and has a good idea what failed. Bulbs and igniters are less than a year old on both sides. Nothing else has been replaced, yet.

Thanks!

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Mike

2005 e53 X5 4.8is 169k miles
2018 f90 M5
2018 Volvo XC60