2005 chevy cobalt tranny issue

about 3 months ago our transmission started pouring fluid all over the ground we originally thought that the case got cracked when we hit a pot hole but upon inspection of the tranny by a mechanic and the insurance rep they determined that it was an interior problem and that the crack was bowed out from the gears letting go and bouncing around inside not bowed in like if we hit something and that with out a new transmission its was un-driveable recently we have had to move the car around and my husband found that as long as there is fluid in the tranny (witch pours out pretty quick leaving a trail) that we have all of the gears still and it shifts just fine it seems like all we need to do is get a new case for it but i don’t understand if the gears let go and were bouncing around how the gears seem just fine and it shifts just fine what would you recommend we do