Has it been lacquered? That looks a lot more like flaking lacquer to me than a crack through the base metal.
Syncros stems normally have a high gloss polish. This one looks like it's been sanded, had the decals replaced, then been lacquered over.
As others have said, remove the stem and look inside. If it's just a crack in the lacquer there's no problem. If it's structural, you'll see evidence of the crack on the inside.