Could be the rubber seal on the flush pipe is at fault or the ring nut has come loose. re-tighten.
It could also be the larger nut holding the syphon in the cistern, re-tighten.
Still leaks! then replace the rubber seals on both.
If its just coming from the flush pipe then sometimes smearing a generous layer of vaseline around the rubber seal works.
Rob
Rob
November 2005