If the toilet rocks front to back the seal will fail, Is the flange screwed down to the floor? if needed, pull the toilet install a new wax ring, removing all the old ring, Push down on the toilet to get it to set, bolt it down and add a few small shims to support the toilet, if it dosent leak, caulk around the toilet to hide the shims. It almost sounds as if the wax ring's horn caught on the flange when it was installed. Another thing is to make sure the toilet is set all the way down. Is it the toilet or the water supply line? Been there-done that!