single line brake master cylinder

[johnboy]

Hi ,
does anyone have a picture of the correct layout of the inners of the brake master cylinder for my Triumph 2000 1977. The front rubber- in at the tip, I'm not sure of which way it sits, as the old one was really disintegrated. I have looked at several books but cannot workout if it sits before the metal part or sits behind it. Any help appreciated.
I would like a new cylinder but they are like hens teeth apparently. I also would like to keep it original.