The atf type oil that ford recommended is NOT std atf, it was a particular atf, that was engineered specifically for the T5 version in the cossie(there are 380+ versions).
The nearest is CASTROL TQ-D, it wasn't helped by ford/BW changing some box parts materials during manufacture, halfords sell the TQ-D, about £10 a litre.
No dexron has ever been specified, although dexron 2E is close, it is much closer to a mercon oil.
tabetha