I am away on holidays for the next month without my car so I won't be able to do any more testing in the immediate future. Thanks for your suggestions, I'll pick this back up when I return and will post an update then.

I will check again to confirm I can feel air through BOTH defroster vents, but I'm 99% sure it does. You're mostly correct with the operation of the controls. Pressing the top right windscreen defrost button will, all at once: set the airflow to the defroster vents entirely (equivalent of top left &...

Do you have a Driver and passenger temp setting on this vehicle? Defrost setting on the driver's side may not be working. Do you feel defrost on both sides? Yes, I have temperature settings for both driver and passenger, but 99% of the time it is set to the same temperature. I'm not sure what you m...

Recently, my RHD 2010 BMW 135i N55 coupe has had the driver's side of the windscreen fog up almost during every drive. It's exactly the driver's half of the windscreen, the passenger side is unaffected. Using the windscreen de-fog button will clear the fog away but when I stop using it, that half fo...