Thanks Sospan, I fixed it using an O ring splicing kit. I replaced them all while dismantled as the tap was 7 years old. More of a comment on the insane design where any one of 21 O rings and other internal devices can send water down the column and through the ceiling below. Whatever happened to the old top washer assembly.
Personally I hate this “built in” craze in bathrooms, sometimes not so bad if retrofitted and done with thought, but if you want a real challenge, try fixing any built in tap or cistern in a new house where access is often non existent and even if you can get two fingers in there it’s like a nail gun version of an iron maiden inside.
