Some that were replaced by Ford had a tag or sticker on the oil pan. If it were changed by Ford, it would also show up on an Oasis report. Those are only available from the dealer though, and I think you have to pay for them.
I was curious of that too, but no one had an answer for me. How many miles are on your car? My 94 has 95k on it and when I was replacing the rear exhaust manifold gasket I saw a yellow paper tag attached to the dipstick tube with some wire, only about 1/3 of the tag was left and there was no writing at all left on it. I don't know if it was left over from manufacturing 10 years ago, or if the trans was replaced at one point and the tag was left on there then.