In the same cars the radiator cap (Part nr 2383 331) is located under the hood, as may be seen in the image above left and in the images below taken from the earliest Owner's Manual of 1936 (left) and from Parts List B (right).

An interesting point which some readers may be able to elucidate is: if the early star was used until, at least, early 1938, why is it never found in actual cars? My car is from early 1937... why does it have the later star? A possible explanation might be that the elaborate front of the car is the part most likely to be impaired by even a minor impact and in an old car it has likely been replaced by a modern part at sometime in its life, accounting for the scarcity of the early scheme. But even so, shouldn't there be a few around? Where are they? Are all our cars thus not original?