"John E" wrote

Warning: amateur plumber at work...

I now have a leak from the connector to the bottom of the cistern - where
the flush pipe exits.


If your cistern is the "traditional" type, then the leak is most likely to
be from one of two places:
1. The syphon or flush unit is not sealing against the base of the cistern
(internally). This is quite likely from the raving around it has
experienced, but would be constant rather than appearing only at flush time.
The water leaks down the syphon threads below the cistern and appears on the
connecting nut for the flush pipe.
2. The tapered rubber washer is not sealing between the syphon discharge and
the flush pipe.

Recommend you get a new flush-pipe-to-syphon sealing rubber and some
plumber's mait.
Remove the syphon which will allow replacement of the rubber seal to the
bottom flush pipe.
Re-fit syphon with ring of plumber's mait around under the base to seal,
introducing new flush pipe sealing rubber as you do.

Phil