Actuators need to be replaced.
They work off 2 separate motors for opening and closing.
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The main issue, if you open an actuator up, is most of the moving parts that take a huge amount of force and impact are plastic. The toothed gears suffer constant torture for as long as they can and then a piece breaks off rendering the locking or unlocking process impossible.
I tried rebuilding one or two but it never works. The last time I tried to get replacements from BMW they mentioned they old special but the prices nowadays are exorbitant.
Best thing is to watch a YouTube video on how to remove the lock then take it with you and go to a second hand spares place and pick one up. You need to make sure the replacement one matches exactly - you get 5 pin and 7 pin ones I think. Then watch the rest of the video as you reinstall.
It is finicky and you need deft fingers and bendy wrists - as well as a lot of patience.