Consider a local gunsmith.I recently bought a really nice used 686-6, everything checked out, BUT never expected that the barrel would not be parallel to the frame. In other words, the barrel was screwed cockeyed into the frame. Need a LOT of windage on the sight to zero the gun.
Called S&W customer service, the nice lady told me that since I was not the original purchaser, they would not honor the warranty. They would do it on my dime, and turn around would be 8 to 10 months!