Update 2: The passenger was fixed yesterday in the same manner. The microswitch on the passenger side was soaked in the same type of stiff grease, rinsed and lubricated with WD40. It now works, but the drivers door is not working any more, even in room temp.
Can some grease have moved down from parts inside the locking unit onto the microswitch again, or are we facing some kind of multiple error ?
Any tips from experts will be greatly appreciated !