Yes you do - a new syphon unit can be bought from a DIY supermarket or a plumbing merchant.
To remove it from the cistern the cistern needs to be lifted from the WC pan. A relatively easy job.
You can also make a replacement diaphragm from stout plastic - the sort that they make compost bags from - use the old diaphragm as a template. Reassemble...
https://www.youtube.com/watch?v=y4AdckesOlg
Good Luck...
January 2016
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