Because I also own a couple of Douglas Dragonflys, a few years ago I got an American company to make copy Miller distributor caps and rotor arms. They have mastered the art of small production runs from rubber moulds using an original for a pattern. They really are very good and the rotor arms fit tightly on the shaft. However, they are expensive but the company does give good discounts for quite modest quantities. Perhaps the spares Secretary can club together with his opposite number in the Douglas Club and put a joint order in. In case anyone is interested the website is https://www.king-cart.com/cgi-bin/cart.cgi?store=kipmotor&category=Distributor+Cap+by+Part+Number.
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