The siphonic action on my old Royal Doulton toilet (probably installed in the late 1960s) has stopped working and the bowl overfills before slowly draining away. Disconnecting the cisterm I found that the donut washer (internal hole diameter 55mm) has disintegrated and needs replacing. Is it possible to get a replacement rubber seal and, if so, from where? I have tried searching the internet but so far been unsuccessful in finding a supplier. Your help would be much appreciated.

Peter A, July 2017

Just find a local plumbers merchant.
The fact that the bowl is emptying dlowly suggests there is a blockage. You may like to investigate further.

Acp, July 2017