The original Motorcraft filter was FL-2005 (Purolator 25230), but Purolator didn't feel like making them anymore so they had everybody switch to the 400s (and Purolator's 20195). The overall size, thread and gasket diameters are the same, but the internal construction is different: the FL-2005 has an extra ADBV. When using the 400s (and equivalents) without it, the Zetec is grumpy when cold, noticeably more rough and noisy. Therefore, the FL-2005-type filter is a must.
Luckily, some companies are still making Zetec-specific oil filters:
Wix 51315, NAPA Gold 1315, Napa Platinum 41315, Mobil 1 M1-211, K&N HP-1012, and of course Fram's own PH/TG8316
Also, the Napa Platinum 41315 (Wix XP 51315XP) is on sale for $7.54 this month.
(Napa's Proselect, Silver and Gold Zetec oil filters cost more than other oil filters, but the Platinums are the same price)