I can take no credit for this procedure.
I got it from somewhere,can't quite remember, but I think
I read it on a Classic Wing Club page.
As some of you know, the GL1000 etc. waterpump is not rebuildable,
and no seperate parts of the pump are stated in any
Honda parts book.
Some smart guy found out that you can get around that fact.
Here we go:
First; for reference, here are the parts of the pump

...dismount pump from bike

...remove this 3/4 moon clip from impeller shaft
(and keep in a safe place. Apparently it's impossible to find a replacement)

...the impeller shaft will have to be driven out. Hold the assembly-body
firmly in your hand and use a soft blow hammer. If it doesn't do the job (it didn't in my case) insert a suitable sized metal thingie and
use a 'real' hammer. You do NOT want to wack away on the shaft it self.
Mine needed some seriously hard punching to drive it out.

...here it has been driven out half an inch, or so

..from then on you'll have space between the impeller and the pump-body, so you can insert a couple of wrenches and put it up like this.
Then insert a screwdriver on top of the shaft, and drive it all the way out

...shaft removed:
(the black thingie in the body, is the mechanical seal)

...insert suitable punch at a slight angle
(through the bearing at the side away from the impeller)
, and drive out mechanical seal, collars and bearing (on the impeller side)

...from the impeller side, insert suitable sized socket
and drive out the other bearing

...and this is what you have

So here are the separated parts.

Above:
..Big O-ring for pump-body #91356-706-000 (56 x 2.4 mm)
..Smaller O-ring for pump-body #91303-283-000 (91303-KT7-003)(37.2 x 2.3 mm)
Mid:
..Impeller and moon clip
Below:
..Mechanical seal (part of it still on the collar)
You can get this from Honda; (it's a CX500 Turbo part)
Part number #19217-657-023
..Bearing. In the artichle they a designated 6000 2RS. Should be available from any bearing shop. (The original are designated 6000 LU)
..Collar
..Same bearing as above
The mechanical seal from Honda looks like this:

and cost aprox. 55$ (in Europe)
(the artichle also mentions a second seal,(C/R3952)
I'm a bit confused about this, but as far as I can see,
what he's refeering to, is that thing on the left side.
They come as a pair from Honda.
Also the above drawing only shows one seal)
I've ordered the seal and O-rings from CMS and I'll go get the
bearing from a local shop