I've got a rebuilt st400 that has never been in service and has seen no fluid. I have 2 gallons of Valvoline Maxlife synthetic but not sure I should use it.
I have 2 gallons of that fine fluid in my fresh TH400 with another gallon on the side once the car is runing.
I've been using that fluid in both my cars for years. My current 400 in the GS has never had any other fluid, and the 98 Riv just passed 205K on the original transmission.
For any kind of racing or street/strip I still prefer Type F. I don't like the shift quality with synthetic but to each their own....plus my trans builder said not to use synthetic in his transmissions.
I'd go with dexron 6 but not the max life. They add extra chemicals to condition seals and extend the life of "old" engines and transmissions. I will be using the dex 6 in my new 2004r.
Awesome fluid for replacement and even adding in very many trans. Like the Allison transmissions in either Ford and GM diesels. But agree, wouldn’t use it in a T400 trans. Type F is what I run and what TCI recommends in there race transmission.
