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...