Just another thought to help...
Maybe this isn't correct but I thought I would share.
I don't hardly ever use the dark slides and I keep them in a cabinet! I don't change backs that often but if you do then you may need the dark slides available when you are out making pictures. My line of thinking is to keep the dark slides out so as the gaskets can remain at max thickness as, I believe, it gets compressed, albeit just a little, each time the dark slide is inserted. And, from what I've read, light problems develop when the dark slides are out! I've never had to replace/rebuild any film backs yet. Haven't had a reason to do so. Maybe it's time to get them done. When I was 100% film based I operated the same way. How did I do 'dat? With multiple cameras. I found it takes much less time to put one camera down, pick up another than inserting dark slides and changing backs. Time is precious at certain events!
Smiles & Lots of Fun!