The Argoflex Forty is one of my favorite cameras, but I haven't shot it much as it has been plagued by an intermittent light leak. I thought I fixed it several times with layers of black tape over the back, but sunny day photo outings proved me wrong.
I finally figured out with the help of a bright little LED that the light was sneaking by the side of the slightly loose-fitting shutter release button. The inner cone of the camera comes out with the removal of two screws, revealing the shutter release and double-exposure prevention mechanism. I glued a small square of fuzzy light seal material beside the shutter release shaft and that seems finally to have done the trick.
None of the pictures on the last roll through the camera showed any light leaks.