Vbar Tail Drift

I have a minor issue that I am trying to resolve. In the hover the the nose would slowly swing left & right (about an inch each way). Increaseing the gain on the tail helps but I am now up to 110 on the gain. I was going to increase the length of the ball on the arm but then I noticed I was on the outer hole (Futaba BLS251) .

There is no tail fin virbraton & it is a joy to fly. I have checked all the linkages .

Thanks