If the toilet flange was not rusted through and the wax ring was installed right, here are a couple of ideas…is the floor level? does it have a hump in it under the toilet? does the toilet rock? even the slightest movement will break the seal. When you sat the toilet on the wax ring did it sit up about 1/4″-1/2″ off the floor? If not it is not thick enough, get an extra thick wax ring. Make sure the toilet sits all the way down on the floor. DH