Here's what I know...
In your owners manual it clearly says "DO NOT MERCON V" and that you should Only use DEXTRON (Mercon) III.
FoMoCo then stops supplying Dex III to their dealerships and says "No, no, no, it's OK now - go ahead and use the Mercon V".
NO CHANGE was ever made to the formula of Merc V
Here's what I
The people who designed your transmission knew what they were talking about and Ford now says it's OK for 2 reasons;
1 - it's in their
benefit to stock & supply one less drum to all their facilities.
2 - they did this only after they knew
it would have no effect on their warranty responsibilities (all the 4R100 were past coverage)
Apparently, the issue is with the rubber seals. If you have a Stock trans, with the Original Seals, I would stay away from Merc V. If you've had yours trans rebuilt, those seals have been changed and are compatible.
BUT, there have been numerous people who have put Merc V in their stock trans, original seals and all, and report no trouble.
Your Choice, You Decide, those are the facts as I know them