We are trying to replace the push button flush on our toilet. We've got a replacement flush, that includes seals for 1.5" and 2" cisterns, however the diameter of the hole at the bottom of our cistern is bigger, about 2.65cm/2.7". We've attempted to use the 2"seal,with the old doughnut seal, and it's got a small leak. So my question is will a new doughnut seal solve the issue, or is there such a thing as a replacement flush for a larger hole? Help please!