Blue water had been leaking on a Cessna 525B Citation CJ3, and corrosion was found on the seal plate underneath. The seal plate was removed and replaced.

Lavatory fluid is unkind to aluminium. Where it finds a way past a seal it runs down inside the structure and sits there, and what it leaves behind keeps working long after the leak itself has been stopped.

Taking the seal plate and the sealant around it out exposed the structure underneath. The damage did not stop at the plate.