I learned the hard way about leaf shutter timing on my Mamiya 645
I was fixing a Mamiya 645 and skipped testing the leaf shutter after cleaning it. Once I sealed the camera back up, the shutter was stuck open. I had to take the whole thing apart again, wasting hours of work. Now I make sure to fire the shutter a bunch of times before closing the body. This simple habit saves me from huge frustration later on. If you forget this step, you could end up with a camera that won't shoot. Always do a quick function check to avoid this mess.
Leaf shutters on those old Mamiyas seem pretty sturdy to me... I had one that sat for years and fired right up after a basic clean. Maybe we're overthinking the testing phase. If the camera works, it works, right? Spending hours on checks feels like overkill sometimes.
And that same idea works for the whole repair job. Test each part right after you touch it, not just at the very end. Catching a small problem early stops a huge redo later on.