I should have done this update a number of months ago, but the post above worked brilliantly. We were able to reconstruct one pump (by gluing in the magnets and using the cotton trick to hold the bushes back). We put the repaired pump back in the boat and used it to drain the full tanks (damn that water smelt bad)! Just need to repair the other ones now. We did try the manufacturer for spares but it seems as though you can't buy spares for the motor, just the new impellers.
I think I'm right in saying you guys recommend the green impellers right? If so who manufacturers them, I don't think it's Jabsco (they seem to just list the two black ones).