[lensman_nh]

This comment seems to suggest that it's silly to think that there's anything wrong with light passing through the felt. Does that mean I need not worry? That my film shouldn't be affected, fogged?

I don't see light passing through unless I directly shine one, and then only at an exact angle.

Using a flashlight is a very, very touch test to pass. When a precision straight-edge is placed on a surface is as little as 0.001" out of flat with a bright light behind it the gap will appear to be huge.

First thing to mention is you won't be loading film outside in bright sunlight. Secondly the felt will have film stuffed through it. Take a piece of unexposed film and put it in the felt jaws. I would wager you will not see any light pass.

It's your call at the end of the day. Words cannot accurately describe the situation.