From my 70C and 71C (a very early) Service
Manual, "The properties of the oil used in the transmission
are extremely important to the proper function of the hydraulic system. Therefore, it is extremely important that the recommended oil, Automatic Transmission
Fluid (ATF), Type "A", Suffix "A", be used.
The later manual says, "Dexron, Type F, or any hydraulic fluid which meets the C-3 oil specification is acceptable. Do not mix different brands. If engine
doesn't exceed 3,000 R.P.M., a premium grade 30 weight engine
oil is acceptale. SAE #40 and multi-viscosity oils are not recommended."
The later manual was published in August 1988.