Having spent a few hours working on the lick start return spring on my Aero 600 I know for a fact that the spring on sale on ebay will not work in the pre-war 4 speed box. Club spares have the same spring in stock and from what I have been able to find out its for the 3 speed box. With the kind help of another club member we have been able to determine the correct kick start return spring for the 4 speed box and club spares are in the process of getting some made. See attached picture of S6 kick start spring.
Roy
