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!