Through considerable luck and diligence in shopping eBay, I picked up a total of 15 usable plate holders (726/6) that fit my Ziess-Icon and Ica Ideal 9x12 cm cameras some time back; with film sheaths enough to load them all, and 9x12 cm still available in limited emulsions, I can make a nice expedition with my 80 year old cameras. Overall, I've been pretty happy with them, but there are a couple with obvious large gaps in the dark slide velvet that causes them to leak light.
Replacing velvet is said to be easy, if you can get to it; unfortunately, these holders appear to be either soldered or crimped closed (unlike the plate holders for many plate cameras, these use a geometric light trap around the frame opening, no velvet at all on the camera, and thus have an enclosed, double-velvet dark slide slot). Has anyone seen any way to get the velvet out and replacement material in on this type of holder?
I dont see much hope of gaining entry to the Ideal holder but there seems to be enough of a lip to rig an external strip of felt or velvet.
That is why I prefer the double sided holders used on Favorits and Juwels as they are bolted together.
Have you tried leaving the dark slides out for a while and trying to ruffle up the velvet. If it is missing you might try to introduce (poke through) a piece with glue on the back and then trim it flush.
You may have hit the key point, Mark -- with the right tool, I could probably jigger the existing (garbage, nothing lost) velvet out of the slot, and work another piece in. I'll have to examine the one I pulled out of service recently, after identifying one that had a particularly heinous leak, and see if I might be able to fabricate a tool -- straightened fishhook, perhaps, for extracting the old, and something made from hobby shop brass trip for pushing in the new...
I have no doubt I could get into the Ideal holder -- I have a Dremel, after all. The problem would be getting it closed up, light tight and correctly aligned, after repairs are completed. I've got a couple that are too rusty to use; I might have to cut one up just to experiment on...