The first thing you need to do is check your fluid level. My guess is that some fluid leaked out of the cooler lines while the engine was out of the car. If you don't know how to check your fluid level it's simple. The fluid must be hot so after it's been driven, park on a level surface, leave the engine idling, car in park and check your fluid. PS if your worried about damaging your trans. further, just start your car and let it idle for about 30 minutes(maybe 45 if it's cold outside), the fluid should warm up. Report back with your findings.