I just shot my first roll on my new Nikon FE and the amount of each frame overtaken by blackness linearly increases as you go down the sequence of frames on the roll, which is why some photos have a little while others are completely black. Only two frames out of the whole roll came out without it, and only 12 came out with anything visible on it at all. I know it isn't an exposure issue because a handful of them just have a sliver of perfectly exposed stuff peeking form behind the blackness.
Someone suggested that the second shutter could be out of sync with the first curtain, the repair of which would surpass the cost of a new one. Just thought I'd get your input as well.
Looks like your shutter is "capping" - the first section is lagging and the second section is catching up and closing the slit, or some variation of that scenario. It likely needs a CLA.