I have a 2004 1.25 fiesta. Just after I got it in November the engine management light came on, the AA said core plugs needed replacing as the plugs were wet. I took it to the garage, they pressure tested it, found a leak from the coolant and replaced the core plugs. Fine for about 6 weeks, but now the plugs are wet again and the engine management light flashes at times and it is not running as smoothly.

I have read it could be the washer jets, but Ford tell me there is no modification kit for the fiesta, just the focus?

Any ideas as to how the plugs are getting wet?

Say they just put core plugs in wrong they can be tricky bring it back they should fit new ones free of charge

rubber seal corrodes around the jet where it fits onto bonnet........ or mayb washer jet hose?

I have a mk6 fiesta and had this exact same problem, the factory washer jets that come with these models are prone to leaking in the rain. On mine it leaked through the back of the jet, onto the air filter and down into the plugs. There are a few options, you can find a guide on here about using silicone grease to stop the leak, or a cheaper alternative to buying new jets http://www.ebay.co.uk/itm/160830422888?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649.