Re: Curious thought on Coolant.
Not just the seal, the bearings themselves are at risk. I'm not 100% sure about ours but many (most?) water pumps have the bearings exposed to the coolant, and use the coolant to lubricate and cool the bearing. Draining the coolant for long periods runs the risk of pitting and corrosion ruining the bearing which will make sort work of the pump.
Where's it leaking? Any chance you could temporarily seal it up?