Andy Dingley wrote:

Use a hydraulic press (or even better, a big manual rack press). A fly
press will press the seal rapidly into place, no matter whether it's
aligned correctly or not.

Thanks Andy, unfortunately a fly press is all I have access to, so it's
a case of using that or not bothering. I've used it before for removing
bearings from driveshafts and while I realise it's vital that
everythings aligned correctly, it does seem to allow reasonable control.
Is the problem you're alluding to, the fact that you can't stop it
pressing too far - i.e. when you're heaving on it, you can't let go
quick enough when the work starts to move?

I'll try the mankiest looking water pump first. So what's the procedure
for dismantling - support the pulley and push the shaft through, then
support the body and push the shaft + impeller through?