ZXR overheating/steaming

[sefer]

Sadly it sounds like you need more that a water pump seal, if there is oil in your water (or vice versa) your going to need a new head gasket at minimum, which of course means taking the head off (and if it's the same as the 250 the tank, air box, radiator, manifold...). Don't let that worry you too much at this stage though, it's actually not that hard.

Pump seal...well I'm a cheap bastard, and while I can't actually remember what I actually did there is no way I brought a new one. What sort of seal is it? A gasket, or a typical rubber water seal?

[TimeOut]

If you're adding water to a hot engine do so slowly and with the engine running.
This reduces the risk of head damage through sudden tempature change.

[awayatc]

Sadly it sounds like you need more that a water pump seal, if there is oil in your water (or vice versa) your going to need a new head gasket at minimum, which of course means taking the head off

Afraid that is the most likely case....allloy heads don't like overheating, and the headgasket is the first thing to go. You will want to have your heads checked as well though (hardness and cracks)
Good luck