I have a 2008 Z4 convertible with an electronic roof mechanism. The problem I am encountering is that the roof retracts into a separate chamber that has not been designed to evacuate the water that accumulates when it rains. So what happens is that the roof motor sits in water and corrodes over time. The mechanic even found a plant growing in the compartment during the last repair. The repairs are about two thousand dollars each time since it is extremely labour intensive to remove the roof and install the new motor. This is the third instance where I have run into this problem and the roof retraction has failed. BMW are aware this is a known problem with multiple failures each year however are unwilling to re-engineer and find a permanent fix to the problem.