Here’s the deal. D1 on my TWO1 is about 25 cents flat on the tuner. The overtone (D2 played w/o the octave key) is in tune. D2 fingered with the octave is in tune. When I add the C# key to D1 the tone goes to crap, but it is in tune. I suspect that I need to open the C key to vent it better by adjusting the felt bumper. Any other opinions or advice for DIY on this? Thanks!