Green Stuff

Screenwash fluid?

Is it oily & slippery?

Your car is only a few years old but I wouldn't discount the header/expansion tank being split (normally by stress fractures on the bottom).

In any event clean and dry the whole area and see if you can trace the leak. A leak in the header tank is not always apparent by the way as it drips so slowly to start with. I ended up drying the whole area and placing tissue under the header tank which confirmed where the fluid was coming from.

Yes it's oily and slippery, does that mean power steering fluid ?

is quite a bright green fluid, sounds more like a leak on your a/c system

Great, AC Leaks sound expensive, and yes silver pipe coming down that area is covered in it, where theirs a join at bottom, am thinking Fords might have broke it when done auxilary tensioner ?

where would I be looking at to check it out and advise / fix, Fords ?, car might have done a lot of miles but is still only 3.5 years old, would have expected better.