I've changed a lot of valve seals in my time, but I've never seen a need on a Duratec.
To do it, you need compressed air, a "vavle hold" tool that applies compressed air through the spark plug hole on each cylinder to hold the valves up and in the head while you disassemble the valve train (followers) and remove the valve spring keepers and valve spring for all 24 valves one at a time while you change the valve seals. I'm pretty sure you need a special tool to remove the valve spring keepers and valve springs. I suspect that it is the same tool I have used on Lincoln Mark VIII engines. On that engine, I was into it to replace broken valve springs, not worn valve seals.
Why do you think you need valve seals?
