bark_eater 

I've seen this line scored on a lot of old stems. The next one I am tearing down had a score mark on the front side of the quill when I raised the stem. I've been curios about the cause. Im going to look at the alignment of the wedge and the actual diameters of the quill and the the stearer id. The previous owner was a big guy and the bike has steep angles and other signs of being ridden hard. The stem is a budget oem model and the rider could have had a lot of weight on the bars, which would certainly be pushing the stem forward. What I worry about is this being influenced by a loose headset and being an indication of an ovalized headtube. I think most stems could be salvaged by sanding out the scores to limit stress risers.
I'll ad one bit of mechanical trivia. When you have a slip fit of a cylinder in a tube, the longer your over lap, the less posible angle for movement or slop. Quill stems are looser than a slip fit and I am inclined to use a longer quill to get as much bury in the stearer as possible.