The murals in the United States Post Office and Courthouse on Grant Street are pretty hard to get to. There’s security, now, unlike when the Department of Treasury’s Section of Painting and Sculpture commissioned the three works in 1934. Two of the octogenerian paintings survive on the 8 th floor; one disappeared. That’s the thing about murals, said Sylvia Rhor, associate professor of art history at Carlow University. They’re large, but they’re not immune to time’s vagaries. They can go missing,