The right (pax) side valve cover has a PCV (Positive Crankcase Vent) mounted on it, connected by a hose to the rear side of the carb spacer. The left (driver side) has the removable cap for oil servicing, connected by a hose to the Air Breather on the carb.
I have photos, but for some reason I can't attach them to my post. :-( Happens to me a lot.
Neil