Mine used to do that a bit before it finally gave out and I had to get another one. If it's consistent, you might possible be able to let it be. I get wind that shifts my dish on occasion and when that happens I usually just have to change the usals setting a degree or two further east or west.... but uh, typically it's a consistent 2 degrees west on all birds or something like that, not one degree on this one, two on that one, five on another. Make sure the pole is absolutely plumb...
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