Do I have to remove the stuffs that the indy put in there last time I took it in for a checkup? Then refill with the new Dexron 3? Or can I just top it up and have the new Dexron 3 mix in with whatever is in there?

From what I know, the indy put in a generic Dexron 3 that comes in a large tank at his garage.

So they can be mixed without adverse health effect right?