[lippy]

As an update, after almost 3k miles, I still have this problem. I have the splined shaft on both ends (latest design) and I've tightened the set screw and nut several times, with blue Loctite. Every time it loosens after about 20 mi. It won't come off the splines so it's not dangerous, but there is extra play, both front/back and side/side. I think what's happening is that the set screw sits on the peak of the "triangles" on the spline, and that peak deforms. Not a great design.

Someone suggested I take the shaft out and drill a small pocket where the set screw sits on the shaft so the set screw has something better to clamp against. What do you think?