I think you would find S&W will not bring a gun up to current standards, if you send it in for warranty issues. If you send it in for a mag drop, they are not likely to tear the gun apart and replace the trigger bar and sear. However if you send the gun in for a sear or trigger bar issue, they would likely replace both with the newest parts. Their only obligation is to make sure the gun is returned to the customer in the same condition, as it was originally sold.

Bob