when you do find these antique leather seals and you want to use them , you are supposed to soak them in the oil used in the application e.g. rear axle fluid for differential seals and engine oil for rear main side seals or timing cover seals before installing the seal , this allows the leather to expand . installing it dry will damage/glaze the seal and make it leak ,. however use modern rubber seals such as Timken 7216
