Duravit Metro ultra low flush

[Ruppies]

Duravit Metro ultra low flush toilet, 22nd floor of condo, 4 cases of massive leaks in middle of night causing damage to units 4 floors down, Flapper was replaced twice previously, when leaks occur there is no usage of toilet within hours and hours. toilet would run for days and then stop and then run and then stop randomly. neighbor below has bad ceiling stains as well. toilet always appears to be clog free and no signs of clogs visibly

any ideas