the vast majority of dealers sell it as Marine-HJ (I suppose to make more money out of it). But it was worn by ALL DJ leaders in a rank of Oberrottenführer as well as my forespeaker correctly states. So these were 10s of thousands, each equipped with a few of them. I hope it wasn't costing too much.
first of all: a very fair price you paid! Congrats.
All these circular black-blue-ish arm rank patches were used by both the DJ and MHJ. Of course, the number of MHJ leaders of a certain rank was tiny compared to DJ boys of the same rank. So, and this hopefully explains a bit better what I wrote in post #3: that's why dealers prefer to declare it "MHJ" instead of "DJ" ... to pull the right strings in the mind of a collector who probably thinks "Wow, MHJ is rare indeed. So let's buy it.".
Attached are 4 pictures with similar rank insignia as yours. 2 of DJ, 2 of MHJ members. Sorry that I cannot provide better pictures right now - these are the ones I was able to find in a hurry.