Here's the state of play:
-heater and gas converter bypassed,
-new radiator, hoses, thermostat and cap,
-pressure tested twice (two different places), no leaks found.

But it still uses lots of coolant: expansion tank empties in about 100km of city driving. I always check it cold, parked in the same level spot.

As I see it, it could be one of two things: something that leaks only when the engine is running (water pump?) and which isn't picked up in a pressure test, or it's going into combustion chambers. It starts and runs beautifully.

The real question is: why does my car have a curse? Or maybe it's me who's cursed?