I agree with Deano56 and the others here, if the tranny fluid was low and ther are no external leaks than the engine is sucking it in, If the coolant was low with no external leaks then I would say look at the top end of the engine for head or intake gaskets.
To crack the bell housing would take an impact or an incorrect installation. You have obviously gone a fair distance so since the tranny was touched by the other shop, so I would guess at a component failure like the others have suggested here check the vacuum modulator.
That may get you back on the road and give you time to hunt for a replacement transmission. I would not drive it far with a cracked bell housing unless you could be absolutely sure the crack will not lead to bigger problems.