I've seen this more on road bikes that go on long descents (lots of small impacts, little steering change to bring in fresh lubrication) and cheap bikes with not enough grease in the headset. Less on off road bikes (more impacts, but much more steering to replenish lubrication). Setting things off by a number of degrees not equal to 360*/number of bearings will help hide it a bit, but replacing the headset is the only cure. The good news is that like bottom bracket bearings, worn parts (in this case) won't further hurt anything that doesn't need to be replaced already. So long as you can handle the bike safely I'd leave it.