Firstly, where is it leaking from? If its from the gasket seals around the water pump body, you can use rtv sealant to re-seal the water pump.
However, if it leaks from the pulley bearing, I'm afraid you will have to change the entire pump.
How frequent do we need to change this LSD oil on our Z33? anybody knows what is the standard specification and type for the LSD fluid? how many litres required? Recently ive just changed my auto tranny...