Yeah, the F2 manual specifically says not to leave the shutter cocked. The F3 and FM2n manuals don't say if you should or not.
Unfortunately, it seems to me that the only way to close this case once and for all would be to store two absolutely identical bodies with the same shutter count for ten or more years, one with the shutter cocked and the other without.
Personally, I store my F2 with the shutter uncocked, since the manual says too. I also store my F3 with the shutter uncocked, since its shutter is similar to the F2's. My FM2n is stored with the shutter cocked since it has more in common with modern shutters such as those found in the F90 and F4, both of which have built-in motor drives.