OK, when changing the reverse light switch I loosened what I thought was the reverse light switch, when I loosened it I got a shock as coolant poured out, anyway I retightened it and all seemed ok but all is not what it seems, I have now developed a tiny leek when the car is at running temp. This thing I loosened looked exactly like the reverse light switch (what you can see from outside of the engine, not sure what the other side looked like as i didn't take it out fully). . . . it is like a probe going into the engine block with a couple of wires attached to it, it was even the same nut size. Its screwed into the block right opposite the battery. I've tightened it as much as possible but still has leak, maybe it needs some kind of sealing compound? Any help on what it is or how to stop the leak much appreciated, can't drive the car now and miss it already!!