My 02 had one, basically a large ping pong ball, for rollovers, but it was part of the tank's neck, not the tube. If we have a filler cap, why do we need such a thing? Extra safety I guess. I remember a YT video on repairing an early EXT's tank with a broken inlet and it was mentioned that you lose this rollover valve with their fix using brass parts. Maybe later years they moved it to the tube itself.