Egad! The last thing you want on any gun is a crack!
Whether wood or metal, what appears as a fine crack opens up in pulses as the gun vibrates during firing. They will *always* spread farther.
It's not a super load-bearing part when the cylinder is closed, but it does hold the mass of the cylinder and ammunition when open. If you ever let some goon try it out and he flips the gun closed with one hand, you may see it go flying. You're sure that is a crack? It's hard to photograph a hair-line, so some people might tell you it's just a scratch.
You bought it new; that defect would be un-acceptable on a used K Frame, let alone a new Performance Center! If it breaks later it's not just a drop-in replacement. The crane is fitted to the cylinder and frame, among other things setting the gap at the forcing cone. On a tuned PC revolver that gap is minimal, and the whole works turn like silk. Aside from getting what you paid for, you should fix it now while you know the factory has the parts and a competent repair centre. While not very likely, if you use it a bit then put it in the back of your safe and it breaks in a few years, they might start telling you ‘Oh those models are hard to service now.’
Marks on the frame seem to be from overly enthusiastic stamping of that deep, deep ‘986.’ Something I'd live with if it were the only problem.
[EDIT] You're the one with the gun in hand; you say it's a hair-line crack that's what it is, but be certain. (Told ya it's hard to photograph cracks.)
