How can I fix my toilet?

I have a Roxby pedestal toilet J/77/400 (which doesn't look as if it has a float in it?? Looks quite complicated inside!) Water has started to run constantly down the back of the pan into the water at the bottom. This causes the macerator to activate every couple of minutes. There is nothing wrong with the macerator (this has been checked by an engineer) but I need to stop the water running down the back of the pan. Can anyone help me please?

Sally
July 2006