Have you taken the fuel rail off and inspected the seals between the rail and the head - this is a known fault, and ford dont offer replacement seals - in their infinite wisdom, they were only ever available as part of a complete inlet manifold (along with injectors etc) - for around #850!!!

A trick some people have used with varying degrees of success is to remove the seals, soak them in boiling water,freeze them, then repeat a few times - and sometimes they'll revert back to their original shape. Job done.

Remember to depressurize the fuel rail before you remove it - just pull the relevant fuse for the fuel pump, and let her idle til she stops.

Let us know how you get on, and hope that helps?