p.2 #1 · Storing Your Leica Camera & Lens: Best Practices
I read about storing manual focus lenses at a mid-range aperture many years ago when it was discussed for Canon FD lenses. I don't think the brand or the lens type matters - I had a few old SLR lenses which were stuck a bit when they were stored with wide open aperture at room temperature for many years unused. I don't know how it works with more modern DSLR and MLC lenses - on my Sony MLC, all lenses remain with fully closed aperture mode when the camera is turned off. This might relate what @cbass mentioned earlier.
I put some recyclable drierite packs in my safe box with camera equipment to limit humidity since it can accumulate in a closed safe. But I admit that I often forget to reheat the packs and re-activate them . But I also keep my home well tempered through the seasons avoiding humidity build-up in rooms.
p.2 #2 · Storing Your Leica Camera & Lens: Best Practices
I've only taken apart a couple of M-mount lenses (Elmarit 24 and Summicron 50 vIII) but neither had spring-loaded apertures, nor would they be necessary when there's no linkage for the old "preset aperture" of some M42 lenses, or the SLR-like mechanical interfaces for in-camera control, where you have the option of focusing wide open and having the lens/camera stop down when shooting. That speedy response requires a spring-loaded design. The M-mounts only need a friction-based diaphragm. The position in which they're stored shouldn't matter because you're not putting any pressure on any part of the aperture regardless. And, of course, most SLR lenses go to their relaxed positions once they're removed from their cameras/adapters, so it's only a concern on the ones that don't.
In my experience, absolutely no use is only second to heavy persistent use in crap conditions for ways to kill the joy of a fully mechanical lens. But only one of those methods gets you memories. Use your lenses. Even if it's just taking them out individually for an evening stroll once every couple of months. Use 'em or lose 'em.
. But I also keep my home well tempered through the seasons avoiding humidity build-up in rooms.