There were a number of German officers in Argentina pre-1914 (and after). There's been an article on some of them. The Germans sold the Argentines a LOT of weapons (think Argentine Mausers, bayonets, Krupp artillery etc.) and a German military mission was sent to train the army with the weaponry. My guess is that you also find an article out there about Germano-Argentine Diplomatic relations during this era as it cries out for some PHD student to have studied. The Argentine records are still extant and rather complete-IF you can get access. It might help to have someone local to do the research though.