The only thing to leak in the bell-housing is the oil pump--either around the outer O-ring (which it would always do, and a slow leak), or past the torque convertor shaft seal. This is probably the culprit and likely caused by a worn front bushing or the bushing is hanging up. It serves double duty--one is to keep the torque convertor centered, the other is to keep the oil pump mostly 'sealed' on the input shaft side. This bushing is a very close fit around the torque convertor shaft and interference fit inside the oil pump. The high pressure oil inside the pump is 'throttled' across this bushing so the elastomer lip seal around the torque convertor shaft 'sees' no pressure as the leakage past the throttling bushing is vented back to the tranny sump thjrough a drain passage. If too much oil leaks past the throttling bushing, the radial lip seal gets too much pressure on it and oil leaks out at a significant rate. Failure of this bushingis apparently very common. Dealers replace the entire pump ($350 part) even though the bushing is available ($17) because the bushing often works loose in the pump and a new bushing will not hold in the worn bore.