Hi. I am needing to replace my yaw arm too. What happens when you use a hex key to unscrew in the place shown in your first photo? Is it that that shaft unscrews from the upper yaw motor housing leaving the shaft sticking up like picture 2? Is is possible to just get the cover off without the shaft? I guess that is what you would have done if you could but I needed to ask because my arm is broken by the roll motor. It all works, I just want to put in a new arm if I can. How did you do with all of it, did you have to re-calibrate? was it successful? Cheers.