The overflow in the toilet cistern is constantly dripping to the outside. The mechanism within the cistern is plastic. I have replaced the rubber diaphragm and 'O' ring within the plastic cylinder, adjusted the plastic stop, but after a while the water seeps in and eventually enters the vertical overflow pipe. The plastic arm linking the float to the cylinder has six round holes, each the size of a five pence piece, roughly. In the fourth hole from the float, is a red plastic disc, held in place by a plastic split pin. Can someone please tell me what this does and can it be moved to another hole? Is this likely to be the problem? Any further advice would be very much appreciated. 
