Roll up some toilet paper and place it on the back of the bowl. If it gets wet then there is probably a leak from the flushing unit. Apparently there has been a problem with the grey flush sealing washer which seems to get bubbles after a few years reducing the effectiveness of the seal. To get into the cistern push the half flush button down and use your nail or a screw driver to lift out the full flush button which has a small notch in it. Next pull out the half flush button. There is a central screw which you undo and that will allow you to then remove the central mount and lift the lid off the cistern. Turn off the water and then use the button to push in the hole on the top and flush the toilet cistern so it empties. The central flushing unit has two plastic clips near the bottom, one on each side. If you push these in using one hand on each side and at the same time lift the central unit it will lift out. Remove the washer off the bottom of the central unit, it simply peals off, and replace it with a new one. You can get new washers from plumbing supply shops. Push the central unit back in place. It will click in on its own. Then turn on the water, replace the lit and screw in the cap before pushing in the flush buttons - good luck.
Bev
June 2009