In 1966, Aldis & Co., which had managed the building for the Brooks estate for 75 years, was dissolved and the Monadnock was sold for $2 million ($ in dollars) to Sudler & Co., owners of the John Hancock Center, the Rookery Building, and the Old Colony Building. The new owners again modernized the interior, installing carpet, fluorescent lights, and new doors, and undertook a major effort to shore up the north wall which had sunk during construction of the Kluczynski Federal Building across Jackson Street in 1974.