We used just about everything in our 727 over the years.

Store brand type F
Name brand type F
Dex/Merc
Universal trans fluid
TCI full synthetic
ATI 20W full synthetic
JD hydraulic fluid

Changed fluid and filter at the start of each season

And the list goes on. We put about 150 runs on a trans per season. The last 727 we ran for 6 seasons and it finally started to show signs of needing a rebuild (900 passes) We had all the good parts in it though. Billet steel drum, lightened sun shell, 2.10 straight cut gear set. roller bearings etc, etc, etc....

I guess my point is that the trans cared less about the type of fluid than it did about the quality of the parts and proper set up.