ATF+4 is not a synthetic fluid. I'm sure you can get a synthetic +4, but the basic fluid is not. And Valvoline is not the only aftermarket producer supplying it. I believe at work sometimes we have gotten a Castro brand +4, but I'm not sure. Mostly we use Car Quest brand. I have no idea the cost of it, but yes it is expensive.
I have also wondered about using +4 in an older trans as I'm having a 727 rebuilt right now and wanted to know if it would work. After reading this thread and the answers to the question in the thread I started, I will probably stick to dexron 3. I'm also going to ask my builder and see what he says.
