Various artefacts have been returned to the US by two private collectors. It is unclear from the article, whether this followed a request made by Greece, or whether there was any claims over the legality of the removal of these items from Greece.
Greek Reporter 
East Coast, New York, News
Greek Antiquities Return to Greece from New York
Posted on 25 September 2010 by Eleni Bozos
Repatriated from New York, were twenty two (22) silver coins from the area of Abdera and two marble fragments. The antiquities, as a donation to the country of Greece, were delivered to the Consulate General of New York, where they were received by a representative of the Ministry of Culture and Tourism, and were brought by him to Greece. The ancient coins were donated by Dr. Jonathan Kagan and the two marble fragments by the family of Teo Nikolaki and Nikolaos Garbidakis.
The marble fragments are most likely from the region of Athens, Greece and scientific evidence will confirm, as stated by the donators, that their possible origin is from the area of Acropolis. The pieces are said to be a part of an architectural state (crown) and a sculpture (probably part of a female statue).
The following collaborated to make this possible: Services Directorate General of Antiquities and Heritage: Directorate of Documentation and Preservation of Cultural Property (competent in matters of repatriation), the Numismatic Museum and the First Prehistoric and Classical Antiquities.