Two months ago I replaced the wax ring on a toilet due to a strong sewer smel. The odor went away immediately. However it is now back! Any ideas on why? I don't see any cracks in the porcelain, there is no apparent water leaking and the toilet functions properly. The toilet is late '80s and I replaced the ring with an Oatley reinforced standard size (flange is slightly above floor level). Thank you for any input!!