Jim Warren wrote:

snip

positioned on the shaft when the gap between the back of the impeller and
the housing is 30 thou (0.76mm if you use metric). Solder the impeller/shaft
join to eliminate the possibility of water leakage along the shaft and under
the impeller.

Thanks ever so much for typing all that. It certainly sounds worth a
try, so I'll start by stripping the worst looking one. I'm not convinced
about soldering that joint though - that sounds like a recipe for
serious frustration. I wonder if something like Hermetite Red would be
an easier solution.

Good luck!. Though in view of accurate positioning etc, I am not sure a fly
press is a good idea.

OK, I've got the message! I'll see what I can do with a puller. I'd
assumed they were going to be extremely tight so hadn't even considered
it was a job I could do at home.