1991 f150 E40D transmission leak?

I have a 1991 ford f150 4x4 and i noticed a small oil stain on the concrete and i first thought it was engine oil, turns out its tranny fluid! Looked under i noticed a crack in the front side of the transmission, im not sure if thats where it could be from but the transmission shifts good but the only problem is that when i select OD on the shifter it wont move (sometimes) but works perfect when shifted on D. Its hardly leaking just a drop here and there. What could this be?

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