The Mercon V spec caused me a lot of confusion.
I found Motorcraft, Supertech, Castrol, Valvoline all had ATF that was labelled Mercon V.
All of these (including Motorcraft) also indicated that they could be used in other applications. The Motorcraft statement surprised me because my recollection is that Ford advise against using a multi vehicle ATF that says it also meets Mercon V.
Additional to the ATF that are labelled Mercon V are other ATF's that then claim they meet the Mercon V spec.
Now, my understanding is that approved and meets are two different things. If it says Mercon V on the front, it is approved. Valvoline for example sells both an ATF that says Mercon V on the front, and then also sells a multi vehicle ATF that says it meets Mercon V on the back.
At the end of the day, I went with the Motorcraft Mercon V because, apart from Supertech, it was the cheapest I could find and for the sake of a few dollars overall, it didn't make sense to try Supertech Mercon V or anything else.
Garages, including dealers, in my opinion, are less likely to discriminate on this. Worse, they use some additives that bring the generic ATF up to Mercon V. This they do to keep things simple for the techs, hold less inventory, lower cost overall or just have been sold on the idea by a salesperson.
My conclusion is that it's better to buy the ATF that specifically calls out that it is of the type your manufacturer recommends.
I can totally see that some others may meet the spec and that your one may meet the spec for other ATF's.
But the reason is likely as follows. There are x number of additives required in certain quantities. Many of these are common but the thresholds differ.
In attaining Mercon V, you likely attain enough quantities of several additives to meet other standards. Some you don't meet.
But in some cases, you may end up with quite a lot more of that additive than required. This is where the phrase "meets or exceeds" comes into play. The formulation may have a range of additive required. Too much of it may be harmful, it may not.
But just as with our bodies, we need fat, we need carbohydrate, we need salt. There is an upper range of what we need, and then there is too much. It may affect us, it may not. Some people get away with it, some don't.
The ideal is to have what is just right, so I conclude go with the ATF that is approved by the manufacturer as it contains only the additives you need and in the range you need them.
