One problem related to water pump has been reported for the 2004 Porsche 911 Gt3. The most recently reported issues are listed below.
The epoxy holding an aluminum elbow that connects a coolant hose to the water pump (I believe) let go, the elbow worked its way loose from the pump and emptied the coolant from the system out onto the road surface. I became aware of the problem when I noticed that the engine temperature needle had pegged at the high end of the gauge range, after which the engine temperature warning light came on. Prior thereto, the engine temperature gauge had been reading at normal levels and responding normally. I was able to stop without an accident, but I noticed after stopping that the right rear tire and wheel well were wet and slippery with coolant.