I know what it is.. Its the part sitting behind the firewall. Exact same issue I had with my car. I made a thread about it ages ago.
The part corrodes over time as its metal, I figure its the same thing.
P.S the car doesnt need coolant thats just to stop it rusting. Good to see you back thought you might have written off the car/sold it as I spotted it for sale on st george website. weird.
Position of the leak is drivers side about 10-20 in from the side of the engine and about 30cm down and in the worst spot you can imagine.