I have a 2007 Ford Fusion with a petrol 1.4L Durotec engine. I had been experiencing a slight problem with minor hesitancy on pulling away and after changing gears, rest of the time it runs ok. Having decided to replace air filter and plugs, I found coolant water in the valley between rocker box covers, I had been loosing some coolant but assumed it was elsewhere. After drying it out I removed the plugs, it possibly is a core plug problem, what is involved if a garage has to replace a core plug ie is it a major/expensive job. Car has never been subjected to frost as I live in Spain.