Abstract: There is disclosed a method of repairing leaky permeability separatory devices, said devices comprising a membrane in the form of a multiplicity of hollow fibers having end portions potted in one or more resinous tubesheet bodies and terminating in an accessible surface of said tubesheet. According to the present invention, each surface opening communicating with a given leak in a tubesheet or fiber is selectively plugged by applying heat and pressure to the tubesheet and fiber material in the immediate vicinity of each such opening. The openings are first located by sealing the tubesheet/fiber assembly in an appropriately adapted jacket and applying pressure to a fluid in the portion of the jacket volume exterior to the fibers.