There is definitely a minimum size for a car parking space. Check your leasehold document for a structural diagram, it should show dimensions of the car parking space and location. In addition, I wonder if your local council building control has guidelines for car parking space minimum...
Hard to specifically diagnose that the water ingress is coming between the flashing/brick without seeing more pictures or being there in person. But leaks like these are common, and easily fixed.
Should be covered in the 10 year warranty as the flashing should definitely not be failing now. You...