I had the same problem. I took out the flush unit and reversed the rubber seal I found on the bottom. It had worn and was not flat but funnel like into the hole, so turning it the other way around made it flatten the funnel when in place on the bottom seal. I also found there was a small loose end of PTFE tape from the pipe joint connecting into the bowl. This was about 1.5 inches long and was sitting across the bottom seal of the cistern. This meant the rubber washer did not make an effective seal. I removed easily by cutting off this loose end.
Everything now works as intended. This may help you.
SimonP
June 2006
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