I got a new stop from Power Custom's I believe it was. Quality part(s). OP if you are familiar with the insides of the side plate then replacing the cylinder stop, filing it barely enough to fit the smallest cylinder stop cut, and replacing the spring I would opt for that rather than sending it in. However, that's not for everyone and that is fine and I would send her back with a detailed letter/note.

ETA: just saw where you took her to a local Smith. Let us know the fix when you get her back! I got my 629 3" for woods carry and bought it partly because it locks up so nicely; and upon the advice of a long time .44magnum shooter/carry nut.