Perserverence pays off! I finally dug out a significant amount of info on Paul Koster who was, until mid-1931, Electric Boat Company's representative for European sales. His office was in Paris. Of all the "Merchants of Death", Koster appears to be the most honest. One interesting (and puzzling) thing about Koster is that he appeared to be very wary of the Germans and German rearmament but then joined the board of directors of Bergmann in Berlin. While he has been accused of being an "international spy", I suspect that he was simply an "information gatherer" for his own edification and to aid in his sales efforts. Koster was pushed out of Electric Boat, probably by Henry Carse, president of that company. Carse had an intimate friendship with Zaharoff and Zaharoff did not like Koster and was pushing for his dismissal from EB.
I realize that this is far off the topic of this board, but the intrigue of the 1930s and '40s involving the "munitions industry" has become fascinating to me. I hope my enthusiasm has sparked interest in this subject among others, as insufficient information has been gathered and published on the topic. And it certainly has bearing on the rise of the Nazi Party in Germany.