Mine went at 120k IIRC. The install is nowhere near as difficult as most people think. If I were you I'd buy the parts(new water pump, water pump gaskets, coolant, opti) and put them somewhere in the garage in case you have catastrophic opti failure(IE the rotor explodes...ask me how i know about this one
). But like Jon said, no reason to replace it before you start to notice problems.