I used Nikon manual cameras all my professional life. These cameras are built to last, and I never worried whether they were put away with shutter cocked or not. As they tended to be used day in day out, being left cocked for long periods did not really occur.
I don't recall shutter problems with any of my manual Nikons. they are stilll used, although less intensively now I'm retired. I recently had the mirror box foam cushioning replaced in my old 1970's Nikon F. I asked the technician to check the shutter speeds at the same time. They were still within tolerance, despite never having been checked before.
Now that's what I call a camera!
Even though stress relaxion in steel at room temperature is a relatively insignificant issue most of the time, it is inevitable.
A test showed for example (I no longer remember where I've seen it) that air-rifles lose a bit of their muzzle velocity with a given projectile when they are stored in a tensioned state for extended periods of time (6 months), compared to the same type of guns stored uncocked. Watchmakers often put a new mainspring in an older watch when they have trouble accurately timing it after a service job.
I store all of my cameras and shutters uncocked. When shooting during the day I advance the film on my 35 mm cameras after each shot not to miss any action, but release them before I put the camera away at the end of the day, with my LF shutter I only tension it before making my exposures. I treasure well-running camera equipment, so doing my best to take good care of them is only natural.
One of the first things I check when handling a second-hand camera in case I'd like to purchase it, is whether the shutter is cocked or not. Shutter springs can get weaker over time in my experience (at least those in the Rollei TLR shutters sometimes do, weak mainprings are a common reason for shutters to remain sluggish even after servicing them).
However, the manufacture of (shutter) springs is not black art. With patience it should be possible to find a shop capable of making a new one at a reasonable price.
Long live these beautiful tools!