It's actually a "touchier" subject than you'd think....
So first, the non-touchy, sure - Valvoline is just fine (I'd consider their Max Life over Mercon V though)
But now here's the controversy...
When your 4R100 was made the Owners Manual said, Very Specifically, DO NOT USE MERCON V in this transmission (from the guys who
made your transmission - look it up in your OM). The later, after it was in Fords best interest to condense the number of fluids they had to stock, and Years after any 4R100 was still in Warranty, they said "Oh forget that, go ahead and use it".
Here's a good link to the discussion here ->
You Just Bought a 7.3 Now What.......? (about 1/2 way down)
What we've learned since then, since the announcement that Ford (and everybody else) discontinued Mercon III and we all felt there was something "fishy" about them changing their position on using MercV (and
Who's best interests was it in to make that change) is that our fears were proven to be somewhat unfounded. Turns out, the concern was for the softening of the rubber seals in the trans and now it might be moot. Our 20yr old seals are well past being softened at this point (for those who still have their original transmission) and rebuilt transmissions all use upgraded seals that would tolerate MercV now.
So it's an Old can-of-worms, but no longer a consideration I think
