It seems that all oem insert mounting bars crack. So long as at least one end of the bar is still attached to the louver you should be ok, you still have the two end mounting holes to stabilize the insert. Someone told me that the Repro louvers seem to be better made in this regard but I have no personal experience with them.
Yes, I am talking the turn signal inserts. I was thinking that when mounted the cracks might disappear when tightening down the inserts screws to the hood but actually I have a feeling it might pull on the crack causing it to open up even more.