I don't see why we couldn't use Mobil 1 synthetic ATF (or any other synthetic ATF). The main difference in type F and Dexron is the friction modifiers (for the clutches), which should make little difference in the power steering system.
Type F is an obsolete fluid anyway and any synthetic should outperform it in PS systems. The PS pump for Duratecs is mounted inside the "V" and gets little cooling other than the auxiliary tube cooler, so syn fluids seem like a logical choice.
