That happened to me with a 3" M13. The cylinder was stuck and the gun was tied up until I had a gunsmith look into it. I asked him what he did and he said that he gently tapped the cylinder open with a rubber (or was it a wooden?) mallet.The story as I know with the M modification was some police agencies ( this applied to all L frames as I recall) could potentially have the gun lock up when shooting full house magnums and the problem was referred to as primer flow- the hot load would cause the primer to back out some of the primer cup deform and get lodged in the firing pin bushing, preventing cylinder rotation.
Unless the gun is depended on for defense with magnum ammo there is no need to send it in. As others have mentioned it was an isolated problem and a lot of non M guns have not exhibited any issues. If it were mine I would NOT send it in.
It functioned fine after that.