Often, on close coupled toilet cisterns, a small leak can come from the low pressure joint between the two units.
The seal around the supply tube from the cistern is a round squidgy washer (donut washer) pulled down tightly by a metal plate - the force coming from two Bolts with Wing Nuts - one each side, pointing down at the back.
You can often cure this sort of leak by just tightening the wing nuts.
Tip - squint sideways along the join line - the donut washer should be thin and parallel - barely visible - if it's not parallel you will have great difficulty making an effective seal without removing the cistern.
Peccavi, November 2009
