Q&A

 Master

This is just a guess. I looked at my information and see no fill plug on the gearbox casing at all. Some Mazdas around this time you removed the speedometer drive and filled the oil through that hole. The upper edge and lower edge of the speedometer gear is the maximum and minimum oil level. I show the transmission uses Mercron R fluid.
Hopefully someone with Ford experience will see this question and answer it. Call your local Ford dealer service department they should be nice enough to tell you.