Sure the oil wasn't inside the spark plug wells? That's quite common and would suggest you need a new cam cover gasket.


The plugs don't look to be gapped the same either. Maybe you are getting a poor spark on the black ones which look to have a bigger gap, hence the sooty appearance.


Zetecs don't seem to like aftermarket plugs, put a genuine Ford set in(similar price to any others), and I would also recommend a new set of genuine leads if they haven't been changed, they should have been done by 100k.