Dee Jay

Hi all, I started my Vitesse MK 1 up this morning only to find a bad oil leak coming from the nut that holds the oil filter housing on, original type housing. Does anyone know if there should be a washer behind this nut and if so where I could get one? As the housing itself is over 50 years old it may be a case it needs replacing, if so does anyone have any idea where I might get one? Thanks in advance