[Oldsguy]

Dexron most likely. Most people agree that all GM transmissions use type Dexron and Fords use type F but to be honest a transmission will use either type it is just best to not MIX them. So, probably the previous owner used Dexron so you should. If you are going to flush it out completely change the filter and fill with new stuff you could probably use whichever type you want. I understand there is a friction coefficient difference between the two, supposedly type F has a higher one.