Update on my centerlock rotor issues. I tried tape, I tried Loctite 601, I tried threadlocker. It helps but it doesn't solve the issue. Incidentally, I talked to two friends of mine who both only realized upon me asking them that they also can make their centerlock rotors rock back and forth on their hubs if they try. It really seems to be a centerlock problem that everyone just agrees to leave alone. Even DT Swiss themselves answered to a guy on a German speaking MTB forum and basically said that it's a problem of tolerances between different manufacturers that is annoying but doesn't pose a security risk and therefore should just be ignored. I have another set of lockrings on the way which I will try together with micro shims and see if that solves the issue. If not, then I'll consider this case closed anyhow. I don't notice it when riding. Braking is fine. It doesn't look like there's wear on either the rotor or the hub splines. I guess it's just another case of the bicycle industry inventing a new standard and then failing to meet its tolerances.