After twice rifling through my spare parts box and failing to find anything that would fit, I found a small opaque bag at the back of the box and lo and behold it contained a new water pump and gasket.
Unfortunately I had nothing (solvents required) to remove the old gasket with, so I patched it as best as I could, and put the new water pump in place with the replacement gasket over the top. I will have to revisit that and change the gasket properly but for the time being -- no leaks.
The engine works well, no sign of overheating and no coolant leaking either from the heat exchanger or via the block. I think there is a small leak around one of the coolant hoses so I will get them all replaced at the next service. No compression issues so the head + head gasket are both good. I am a bit suspicious about the timing belt, I think the last time I had it replaced was when I had the engine overhauled about 4 years ago so it's due for a replacement (fortunately I have a spare one of those).
So it's all good. I didn't go as far as I had intended over the break, electing to stay between here and Broken Bay instead until I get a proper service done, but I did get some sailing done.
Next job will be to get together with Jeff and some of the Nemesis crew and get some photos done with the new sail wardrobe. Since I had the last set of photos done (and nice they were too, thanks to Hayden and Tony), I have had a complete sail wardrobe change, with new headsail and staysail as well as a new cruising spinnaker. I'd like to get some shots out on the water with all of that up.