I had the mainspring go south on one of my Smiths; it's not common, but any spring can fatigue on not be made correctly. I had a number of mainsprings in my 325 alloy .45 too; they were all theoretically the same, but some would fire reliably and others not. There was a couple thousandths difference in thickness.
I would try calling Smith; their customer service is second to none. They may well send you a strain screw.
I wouldn't over-think any other issues the gun may have, if the action works smoothly and doesn't feel gummy.
Actually, Smith might even want you to send it in on their dime. They have treated me uncommon well.
Moon