My water pump bearing suddenly failed to the point it rattled and coolant went everywhere. I can only assume that it had been leaking via the bearing for a while since I had seen spots of dry coolant on the underside of the bonnet. The local dealer replaced it for around £150
I had a similar problem with my 3.2V8 Sport, although I didn't get restricted performance: a dry joint with the main supply cable to the PCB in the control box in the engine bay. This requires removal and going over with a soldering iron. My local dealer did this for me for a very reasonable rate and the problem has not come back