I’ve noticed a little rust mark on the engine pan, right under the raw water pump, for the last while. There’s been the occasional drip, and I was getting ready to take the pump off and check the gasket and impeller as part of the routine maintenance.
Last night, as I tidied up from the work on the heads and electrics, I lifted the companionway grate to clean out the dust, and there was water in there – more water than could be explained by me coming in and out of the boat. Shone a light at the stern gland, and it was dry as a bone, which meant it could only be coming off of the engine, or down via a locker.
Checking the engine was easy, take the companionway steps off.
Engine off immediately after getting the footage captured – the pool of water in the engine tray is not a good sign, but the fact it’s not overflowing is also a good sign. Looked in the bilge (which I hadn’t done for several days), and found it about half full.
Looking from under the pump, towards the starboard forward engine mount 
It shouldn’t be green; at least one pump design used a copper alloy, and I suspect mine is that variant
Definite signs that the water is leaking down the core spindle of the pump, around underneath, and on to the jubilee clip. Said jubilee clip is covered in corrosion and salt, so this has probably been a slow leak for a while, and has now turned into a faster leak.
I need to confirm whether this is an original pump, a Johnson pump, or some other replacement – there are several other Johnson spares on board, but the pump is Yanmar grey, so I’m not sure. Only one way to know, take it off. My worry is that if I take it off, the hose from the pump outlet is looking a bit perished at the hose -> spigot join, and it might not want to go back on.
If it won’t go back on, I’ll have to get Blue Opal towed to the club pontoon for shore power (or the marina, but the club is free), since I need to keep the batteries topped up to power a CPAP machine.
The water has been draining out of the cooling system for all of last night; more water had run down into the bilge. Blue Opal has a calorifier, so there’s several metres of hose to/from it, and goodness knows how many metres of pipe inside the calorifier, all full of raw water that’s happily draining out through the pump spindle.