So I'm going to go out on a limb here and say that the tranny likes Mercon V more than it does the (non Mercon V) Mobil 1 fluid.
I guess this proves you can't use Mobil 1 ATF in everything.
It would appear that Mercon V may simply be "better" for this application than a universal ATF.
I remember that at one point, Mobil 1 ATF was approved for Mercon V applications.
Is it no longer?
Not according to the PDS
Mobil 1 Synthetic ATF is also suitable for use in vehicles that specify the following fluid requirements:
Audi G 052 025-A2, G 052 162-A1
Esso LT 71141
ETL-7045E, ETL-8072B, N402
Ford* MERCON*, MERCON V, MERCON LV
All 2005 and earlier GM vehicles**
Hyundai SP-II, SP-III
Kia SP-II, SP-III
MAN 339F, V1, V2, Z1, Z2, Z3
Mazda ATF-III, ATF-MV
Mercedes-Benz 236.1, 236.2, 236.5, 236.6, 236.7, 236.9
Mitsubishi Diamond SP-II, SP-III
Nissan Matic-D, Matic-J, Matic-K
Toyota T-III, T-IV
Voith 55.6335.XX (G607, G1363),
ZF TE-ML 03D, 04D, 09, 14A, 14B, 16L, 17C
*Not recommend for
CVT applications, Mercon® SP, Ford Type F
**Mobil DEXRON-VI ATF is recommended for 2006 and newer GM vehicles and improved performance in 2005 and earlier vehicles, wherever DEXRON is specified