Simple as far as I know you can't it is a replace job but don't take my word for it ask in a plumbing outlet Not a DIY store they wouldn't know unless a retired plumber works there to suplement his/her megre state pension.
Rob
April 2008
I can answer this question...
China water Flush Tank Cracked for no Reason and Dripping How to Mend it?
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix toilets.