Tranny leaking from seal between engine and tranny

[4DR99']

i'm new to the ranger scene and have a 1999 xlt w/ the 4.0 and auto tranny. my sister in law had been driving it two states away and it recantly started leaking transmission fluid onto the cat. i thoughgt it was a bad gasket so i had the pan gasket replaced and it continued to leak so she brought it back infor an opinion. i'm not in the area so i can't look at it personally untill she comes back down at the end of the month but the guy said somehting about the metal corroding and i believe the seal between the engine and tranny has popped out of the grove its supposed to be sitting in but he was able to turn the metal/rubber seal to sit better but because of the corrosion he said it will fail again. he told me i will need a whole new tranny is there any alternatives i can do to stop the leak? is it somehting i can fix once it gets back down here? anyone have experienced this before? any advice would be great thanks