A few days after the diesel-water incident, my engine siezed. Despite my efforts to run diesel back through the engine, enough water remained to sit inside a cylinder and rust the piston in place.
It was completely stuck - I even broke the starter handle trying to turn it over.
The first thing to do was to remove the injectors, and pump CRC (WD-40) into the cylinders. Unfortunately, the rods holding down the injectors were rusted in place. My mates Chris & Clint came over to help, but we stripped the threads trying to remove them.
Following their advice, I welded nuts to the top of the rods, and flushed them with penetrating oil. A few days later we managed to get them out and get access to the cylinder.
I poured a bunch of CRC in every few days for the next week or two.
While this was going on, I also cleaned out the raw water system (zinc oxide had been building up and blocking it, causing overheating), and replaced the anodes.
After a couple of weeks of this, it was time to try and get it unstuck. We had trouble getting enough leverage to move it, and tried several different tacks (poles attached to wrenches, crowbars, dyneema on pulleys, etc), but I eventually found a huge old antique pipe wrench (Trimo, 70-100 years old) in Dads shed which did the trick.
After some cleaning up we managed to get it turning over normally, and could even get it to burn ether. I also made a groove on the part where the starter handle connected with an angle grider, so that it could be used with a wrench. It still didn't run, however.
It turned out the inejectors and high pressure fuel pump were also blocked. Water is heavier than diesel, so it sat in the high pressure pump at the bottom of the fuel system - after the fuel filter. Diesel bug (bacterial biofilm) built up while I was working away on getting the cylinders unsiezed, and when I turned the engine over again it made its way though the rest of the fuel system, blocking the regulator valves on the HP pump and the nozzles in the injectors.
I took the injectors apart and cleaned them thoroughly, but cracked a banjo bolt connecting the fuel line. I replacements on the lathe from M8x20 bolts.
The high pressure pump was the last thing to be done. I had originally misdiagnosed the problem as being purely the fault of the injectors, but turning the engine with the fuel line squirting into the air exposed the issue. I got the water out by blasting alcohol and compressed air through the pump, and cleaned out the chunks of biofilm by disassembling the valves.
Success! I still need to do an oil change, as there's lots of kerosene and CRC in the lubrication system at the moment, and after a long run will do another change + replace the filter, as a lot of loose debris will probably be dislodged by the CRC.