I am trying to work out if the top cap on these carbys is supposed to have a gasket or 'O' of some sort?

All the exploded views of the carby I have and Bruce has uploaded shows nothing there but the cap has a grove that looks like it would take something?

You would think it would have one otherwise dust will get in!

Below is a pic of the cap I am talking about.

Thanks

[Linked Image from i256.photobucket.com]