help with flange

[Stuart]

Pulled today the flanges of my 1303 1979 "vert" to replace them by 181 flanges. When I had the VW flange in my hand I saw some kind of thin metal ring on the backside of the flange. Is this a part of the flange or a seperate sealing ring of sime kind. I saw that the 181 flange had a similar ring but it was bend a liite bit against the flange. It this a replacment part? Every help welcome.