I am really enjoying this topic as Dutch Lugers are one of my favorite subjects.
Albert asked why the Dutch went to a slotted cleaning rod. I suspect it was because it would hold the cleaning material more securely than the jag type tip. When I got my holster, the cleaning rod was in it and still had a piece of cloth threaded through the slot! (Made it a bit tough to pull the rod out the first time). It could be that it was carried this way to be able to make a quick swipe of the bore while in the field.
The Japanese connection is true in some cases. On the inside of my holster is the name of the individual that acquired the gun and holster in 1945. There is no rank listed, so I don't know if it was an American GI or an Aussie or what. But on the back is evidence that probably it was obtained by convincing a Japanese soldier he didn't need it any more. If anyone can read the inscription I would be most pleased to know what it says.