OK, here are the photos:
OK, well it looks like that slot is an atmospheric vent to allow free movement of the diaphragm…But, I will freely admit, I have never successfully rebuilt one of these little pumps, my vision is too bad, hands too shaky, to ever get those little pieces back together properly again….Someday I will conquer one of these little buggers!
In any event, I would certainly contact the seller if you paid $68 for this leaky pump! He should refund your money, or at least give a partial refund if you successfully rebuild this thing.