Help diagnosing 7x17 light leaks (not a newbie, but still)

So, I finally got my 717 going and just developed some negs, and about half had some sort of light leak. The holders are s&s and the camera is a folger and schwing w a back tailor made by Ritter to match these holders. In the more severe leaks the back was uncovered but in shade, on the others the back was covered by the dark cloth but in full sun. All the leaks occur on the flap side fwiw. I'm guessing it's my technique when pulling the ds, though I made it a point to hold the back down as well as keep it covered, so not sure what's going on.

do you feel the rib locks engage with the back when inserting the holders ? second photo looks like holder not inserted all the way maybe ?

fwiw, I have original holders and newer AWB for my Korona 7x17 and haven't experienced leaks like this.

Good luck sleuthing the cause ;)

The holders lock down really well, as I said, the back was made for them. But that's one of the shots where the back was uncovered, so either the fit isn't quite as tight as it shld be or I did something wrong when pulling the slide or replacing it.
I should also mention that I tested the holders w paper and had no leaks in full sun for 20 minutes, but this is 400 Asa film.

Just checking to make sure the back is actually locking onto the ribs. If I don't feel the snap, I usually tug the holder to see if it moves. Will look at my camera later to see if I can see what might be the cause, but sounds like light is sneaking in between the back and holder somehow.

What has your test in a pitch-dark room and a flashlight inside the camera shown you?

Have you checked that the back itself is bedded properly into the main body?

Yes, I checked the back w a holder in it in the dark w a flashlight and no leaks. I'm starting to think it's when I pull the ds, that maybe the back doesn't stay flush when applying pressure. What else can it be?

Do the test again; set the light in the camera pointed towards the back, put the lens back on, and (in the dark, of course) pull the darkslide in and out a few times.

But frankly, the worse of your fogging seems to be out-of-camera, since the rebate is heavily fogged.

Get a wide point black felt pen. Use it on all surfaces on the flap and the area where the flap seats. I had the same problem with these holders, and this solved it.

Vaughn, that's a good point about the rebate being fogged in the second one, so that would mean the film was fogged prior to being loaded? Or at least not while in the holder?