Just to revive this old thread i'd like to add my two pennies.
I have a local motor factors that stocks the ford brand oils, semi @ £18 and fully synth @ £24 for 5ltr bottles. Not sure if these are imported from US or Europe or UK spec.
Having read the user manual it states not to use certain API codes (not a clue about these) and a lot of other branded oils don't meet the particular ford spec.
I have been a member of another car forum (Saab) and they often discuss the whole which is best debate, with a notable bit of info.
ApparentlyUS oils are not as high in quality as european oils and a lot of the garages don't drain the oil they suck it out thro the filler, which in my mind leaves the possibility of a sludge build up in the sump.
Any one have any thoughts on this? Definitive answers? American members want to put me straight?
To finish, my opinion is in the uk, fully synth of the right spec at approx 8000 miles or annual which ever is first, depending on driving style 6000 if driving harder.
Jan