So you have the maintenance manual of the i4...? Turning on the defrost is one thing, of course I see if it works or not, there is nothing more to check there, but by turning on the AC you do not perform an inspection, it just shows that it works now, no warranty that there is no leak or signs of leak in the system. I can't perform that check. I have no idea of the maintenance plan or the contents of service manual of the i4, all I know is that the maintenance plan of ALL my cars I or my wife ever owned had that check done as part of the plan on regular basis.
Same is true for the brushes. I have no idea if that is part of a service plan, for example changed after a certain number of miles, of it has a warning system when they are worn out, or if they are viually inspected, but turning the car on and drive is NOT an inspection, it does NOT say anything about the condition of the brushes. By the way, those brushes are NOT lubricated and of course, not polished. I definitely know that much about them. It is possible that they will never ever need to be changed, unless there is a material issue in certain batch, but it is also possible that they must be changed say every 100 k miles, but I am sure BMW have figured that out already, and hopefully not just let you drive away from home not knowing if the brushes are fine or need to be changed, not polished or lubricated

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