If you are talking about the 69/70 central oil tank, on page 42 of the "Commando Spares List", under the supplement for the 'S' "oil pipes - page 22", the feed filter washers are 042065 and the return adaptor washer (smaller one above) is 14698. I couldn't find them anywhere, but when I talked to Ella at OB, she went right to the 14698 when I gave her the number and it fit perfectly, but they are copper.
Dave
69S