Waterpump is a major hassle to change which is why they do it when replacing the timing belts. I had the hissing noise you speak of at the front of the intake manifold where a small metal coolant line comes into the back side of the front of the engine - hard to describe - anyway, it enters the front elbow going to the upper radiator hose and there is a o ring that fails in there. I have the part numbers at home for the oring and gasket and it can be done somewhat easily by removing the serp belt and the upper radiator hose manifold. See the VX service Manual CD for info as well. Parts were about $10.

Refill your cooling system and have someone start and stop the engine and you can usually see where the coolant shoots out of the leak. Mine did it more right ater I shut off the engine from driving but I could smell coolant for a long time before that.