WASHINGTON – Jed Leiber was an adult before he learned that his family was once part-owner of a collection of centuries-old religious artworks now said to be worth at least $250 million.Over a steak dinner at a New York City restaurant in the 1990s he had asked his mother about his grandfather, a prominent art dealer who fled Germany after Adolf Hitler came to power. “What was grandpa most proud of in his business?” he asked.“He was very, very proud to have acquired the Guelph Treasure, and then was forced to sell it to the Nazis,” she told him.That conversation set Leiber, of West Hollywood, California, on a decadeslong mission to reclaim some 40 pieces of the Guelph Treasure on display in a Berlin museum.