My 12 year old toilet began weeping between the cistern and toilet base. It was only a minor leak and didn't appear to be linked to flushing the toilet. I replaced the cistern o-ring yesterday and everything seemed fine until today. Now whenever the toilet is flushed, a considerable amount of water leaks from between the cistern and toilet. The original 0-ring (on the left) looks as if it was made from a rubber material whereas the new one feels like some type of compressed foam material. Any suggestions about what is happening and how to fix it? Many thanks. ps The only damage I can see in the old o-ring is a very small nick (at the 12 o'clock position). Would that be enough to cause it to fail?