my sunroof is the same as well as a freinds, they must just be like this in the r34.
any water which gets in goes down the rails in the sunroof and into drain pipes which lead to the ground. if it does leak could be these drain pipes are blocked... happended to me once and my headliner got wet. all i did was take air compressor to the small holes in the corners of rails, blew all the dirt build up out.