the right tranni fluid?

Not to high jack this thread... But after pulling out my driveshaft I lost a lot of my fluid. I had no idea what to buy so I bought ATF+4. Well I then called the place that build my tranny to be safe. They said to use any of the Dextrons. Now my question is... Since I already bought the Atf +4 can I mix the two? I assume they must have use Dextron then when they built it.
It sure seems these trannys can take anything.