11x14 Fidelity holder light trap exposed...to lights and camera, not FELT!

I got 2 very dirty 11x14 Fidelity film holders, one cleaned up ok, the second had serious large light trap light leaks. 1/8" gaps.

I now know why. I drilled out the rivets, not a problem.

However it appears somebody in the past tried to fix something in the trap area with horrible glue, which soaked in the cloth trap material and made it non-flexible.

I think I can save it, if I can find the right cloth. An open weave block polyester, NOT FELT! You can see right through this cloth, but it is used on end so it would be light tight if it is soft enough to conform with the brass spring sheet. btw That spring material is 3 pieces overlapped, not one piece. I bet they simply used 4x5 stuff to build up to larger sizes.

Has anybody else done this successfully?

Which cloth?

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