Pet wrote:
My tip for these PITA inventions is compress them up then undo them and
coat the olive in a healthy dose of Fernox-LSX silicone or similar.

Spent many hours Saturday faffing around behind the newly fixed basin &
pedestal with a tissue trying to find several weepers.

Silicone (as above) and a cup of tea while it cured did the job a treat.

So it's a rotten useless joint, then.