What is this ring for under Caad8 lower headset bearing ?

DCI Gene Hunt
DCI Gene Hunt Posts: 138
edited February 2015 in Workshop
I put my Caad8 on my workstand and removed the front wheel and brakes. After removing the handlebars I slid the fork out and noticed that under the lower 1 1/8 bearing there was a very thin flexible black ring that I assume sat under the bearing and on top of the crown race. I was totally unaware of this washer (?) existence and I cant find any reference to it, would anybody have any idea what it is for ?