Just received the mag release for a 745 and installed it on my old 5906.
I ordered it from Midway. It was initially on back order and I had to wait about a month. Big difference from the original. See the pics on the previous post of the 5945.
I just unscrewed the mag release button a bit on my 915, which works fine. I can release the mag much more easily, and it seems to stay put just like it did before.
I have a 915 and a 39-2, and a friend has a 410. The 915 is definitely more related to the 39.