Ok i just got back from the garage. The guy did a pressure test and he said there are no external leaks.

He said the only other thing could be a possible head leak where some water is entering a chamber (i think he said)... but this wasnt tested. I did mention to him that i was told by someone that they had a similar Mondeo where the water would only want to sit below the minimum mark and if it was higher than that it would throw the coolant out or discard it until it sat at 1 inch below the minimum... the mechanic just looked at me and said 'well, where is it going to get thrown out, its a concealed unit... it cant go anywhere unless there is a leak' to which i had no reply, i just wanted to mention it to him as a possible thought.

He did mention a product called Sol-X which he said is trade only and is the best to seal any small leaks and recommended i buy it as he said it was fantastic stuff that has never failed him before in 8 years, so i paid £15 and he poured it into my filler cap... all i have to do now is just see if it helps at all... i am always unsure that these things will block something that they shouldnt... but he said that wont happen. Any thoughts on all this please?