68 Valiant Auto 3 speed tranny on Slant 6

This morning, my son who drives our 68 valiant calls me and says the car wont go anywhere. It wont go in gear and move. I ask him to try putting it in reverse and see if it might be the drive gears or maybe something else. it wont budge. Then he sends me this picture. What could cause this type of leak on these trannys? Is there a rear seal on the tranny that can go bad? What do I look for once I get home? He had it towed to the house.

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