You can still buy type f fluid. I would contact the trans shop that rebuilt it and ask them. I've only used type f in mine and just had a C6 rebuild by a state of the art trans shop. Never said anything about not using type f.
I stand corrected. I did find an 'autozone' brand type F. It's probably time for a flush anyways.
The trans shop I had it rebuilt at sold to another owner. The new guys don't work on old transmissions. In fact, they don't rebuild the newer models either, they just swap them out. So I doubt I would get a good answer from them.
Transmission is running great, just leaks a little. I need to go find where.
I get type f at Napa. I once needed type f at 11:30pm because we had a transmission cooling line leak on my wife's car. We were going to a car show fist thing the next morning. I found type f that late at night at the local Walmart.