Could a Syphon were the handle is possibly not fitting correctly to the hook cause strain and cause the seal between the syphon and the cistern to leak.
What's the best way of avoiding cracking a toilet pan when screwing down to a concrete floor. With regards to possible over tightening to stop rocking.
Would this old tank valve swap for a part 2 float valve? I'd have to take the whole valve out and connect back on to the tap connector. I know who ever fit it has put the overflow too high.