The tab on the bottom of the rail that rides in the rail slot is worn down and chipped, causing the slide to jump out of the rail slot. I have seen the slides marketed as Type 1 thru 4. I have also been told that they are all the same type regardless of maker or year made. I'm in the dark here?
Please post a photograph that shows the "arm" attached to the "Box" There is a contour there that I would like to compare to my reference. You have two photos that show the opposite side
Incidentally, my ref (Canfield) cites variations 1 through 6 instead of one through four.
From what I see, I am guessing that you have what is listed as an "E279" or what Canfield calls "type 3"- straight cut at rear of the 'box' and heart shaped cam cutout, looks like a narrow arm joint to me. If I am correct, then that operating slide came into use roughly mid to late '43.
I think my ID is right. I also came up with the "E279" independently of the chart, going instead off the designation in the book based on text description, and that meshes perfectly with the chart in this thread.