The directors of the Met suddenly find themselves under intense fire from prosecutors in Italy, who say they have new and irrefutable evidence that the vase was looted from a tomb north of Rome and sold to the museum under false pretences. They want it back. And, while they are at it, they will take a few other things they also consider to have been stolen.
This is only the latest salvo from the Italian authorities is a tug-of-war over ancient treasures held by art institutions and private collectors in America. Their most important target, until now, has been the J Paul Getty Museum in California. It has been asked by the Italians to hand back no fewer than 42 objects in its collection.
Far from genteel, the affair has already led to charges being filed in Italy against a former antiquities curator of the Getty Museum, Marion True, as well as a well-known American dealer, Robert Hecht, who is also at the centre of the newly emerging Euphronios krater intrigue. Both are facing trial in Rome for allegedly trafficking in looted art.
Greece has also got in on the act by presenting archaeological evidence proving the Greek origin of three of the masterpieces of the Getty's antiquities collection. A gold funerary wreath, an inscribed tombstone and a marble torso were all purchased in 1993. The fourth item, an archaic votive relief, was bought in 1955 by the museum's founder, J Paul Getty himself.
Now, it seems, it may be the turn of the Met to come under the same tough and awkward scrutiny. In addition to the vase, the Italians are reportedly pursuing six other items in its antiquities collection as well as eight items in the private collection of Shelby White, a New York philanthropist who is also a member of the Met's board of directors.
How long the krater will remain in New York is now in serious question. The museum has said in the past that it will not take the Italians seriously until they come up with "irrefutable proof" to show that, as they claim, it was stolen from a necropolis outside Rome after 1939, when exporting antiquities without proper permits became illegal.
Prosecutors in Italy may now have that proof, according to reports in the Los Angeles Times. Most notably, they are throwing doubt once more on Mr Hecht, who sold the vase to the museum 33 years ago. He said at the time that he had acquired it from a Lebanese businessman who in turn had received it from his father.
Not so, say the Italian investigators, who offer a quite different version. Citing passages written by Mr Hecht himself in a memoir, they say he purchased the vase from an Italian dealer named Giacomo Medici, who was convicted last year of trafficking in stolen art and sentenced to 10 years in prison. The case is on appeal.
Moreover, the Italians apparently have photographs of Messrs Hecht and Medici posing next to the vase in the Met. (Mr Medici, they claim, travelled the world to be snapped beside items he had found and sold.) A deposition from Ms True may help to support the Italian version of events.
Their story makes no mention of Lebanese businessmen. Instead, they assert that the vase, portraying the death of Sarpedon, the son of Zeus, in a scene from The Iliad by Homer, was lifted by robbers from Cerveteri, the site of an ancient Greek necropolis, in 1971. It was sold to Mr Medici, they say, who in turn sold it to Mr Hecht.
Mr Hecht acknowledged last week that he wrote more or less the same version in his memoir, but claimed it was fiction designed to help the work sell better.
Even Thomas Hoving, the former Met director who acquired the krater from Mr Hecht, is apparently having doubts. He told the LA Times that he considered Mr Hecht's memoir constituted an "important piece of evidence". He went on: "It proves, as the final nail in the coffin, where it came from".
* Elgin Marbles: Chiselled from Athens' Parthenon in 1811 by Thomas Bruce, the Seventh Earl of Elgin. The Greek government has been demanding their return from the British Museum for decades.
* The Axum Obelisk: 1,700-year- old column looted by Italy in 1937 and returned to Addis Ababa in May.
* The Beneventan Missal: A 12th-century manuscript looted by the Nazis and bought by British Army Captain in a bookshop. British Museum agreed to return in March.
* Nefertiti Bust: Brought to Germany by an archaeologist in 1912. The Egyptians demand its return.
* Benin Bronzes: 700 plaques from Nigeria, now in the British Museum. Some were sold back.