Had to send a BNIB 640 back for warranty service before I ever shot it. Just got it back and I'm very pleased with the result. The revolver even looks like a new gun should look now, where-as it didn't the first time I took delivery of it. Anyways, the repair description was:
-replace BBL
-repair yoke and frame

So what I'm intrigued by with this service is how they fixed the appearance of the serial number on the frame. The revolver I sent in had a very botched up looking sn, on the frame in the yoke area. This original sn job looked like it had been done free-hand with a punch, and then dremeled deeper. It also appeared to have been redone over smaller letters. The metal was puckered up around the barely ledgiable alpha-numeric digits which were deeply set.
NOW HOWever, not only is the serial number less than half the size of the original, it looks lazer sharp perfect, AND the surrounding metal looks flawless. There is no evidence of the metal having been reworked at all. I'm told that they did not replace the frame. Can someone explain to me how they could have done this? The only clue is that the metal around the sn is now unpolished and darker than it used to be.

They probably replaced the entire frame, and just stamped the old SN on the new frame.

That isn't how they handled it when they needed to replace the frame on a revolver for me. New frame, new serial number.

They told me that they would be required by law to inform me in advance of replacing the frame, and it would include a new transfer because they have to use a new sn on the new frame.