Water leak in my AU wagon

Hi All

I purchased an Au wagon 18 months ago from a dealer in Perth. Luckily I got an extended warranty, yes I know there not much use but in this case it was for the best. I got lots of stuff fixed under it but had to pay for the rest. The car is dual fuel and I've tuned it for gas and use the gas oil. I've had the spark cables replace with high tension ones, replaced the crack air box, had the flooding problem on the front passenger side, the rear that sometimes unlocks when you let the front door slam shut, the cruise control that doesn’t, the air pipe into the carby burst open due to backfire and assorted small thing that I have solved.

But here’s the BIG one. A constant (as in it's always happening) but erratic (can happen 3 days in a row then not happen for 6 weeks) water leak in the cooling system. I have replace the reservoir (small crack) had all the hose clamps replace with tighter ones, cleaned and remounted the thermostat hose and pipe. And still the thing leaks! And the way it leaks is the frustrating thing. There is no pattern to it, it'll be fine for weeks and then suddenly go down over night. I have witnessed this, once I checked the car after it had cooled after a long trip, fine no problem. The next morning the reservoir was almost empty! One very cold morning before starting it I checked the it and found a drop of coolant under a metal pipe that ran into the engine directly below the thermostat housing, there was no coolant around the thermostat but the metal pipe had a small amount. But the engine holds about 5lt of the stuff but I've never found a puddle under the car. I just seems to vanish. An internal leak has occurred to me but the car seems to be running fine, some mornings it can be a bit rough. The car has had a small front ender, the source of many of my problems I think.

This water thing is driving me crazy. Can anybody help?

Eldarau