I am replacing rear brakes on '71 Series IIa. Hub seals were shot and gear oil had leaked all over the inside of the brake drums and looks like it saturated the brake shoes. I read in another forum from Australia that the cast iron of brake drums is porous and would soak up the oil and therefore need to be replaced. Is this the case? Given they surface gets very shiny it seems like it would be hard to penetrate the metal. One post suggested soaking the shoes in gasoline and "burning" off the oil!! Thanks for any help in advance.