I have read about the black pepper and I am going to try it, although the leak is minimal. I am also considering some of the chemicals available as radiator sealants. In any case, if I have to remove the rad again, I will take it to a specialized workshop, because I feel that everytime I remove and reinstall such an old and delicate item, a weld cracks or worse. It is quite important for me to finish the restoration of the cooling system because the grille is fixed to the rad bracket as well as the bonnet, the headlamps are attached to the grille and so on. Fortunately the pump leak is solved and the old lower hose has ended the leaks I had to suffer with the steel tubing.