No loctite or glue needed but they will go on part way and seem like its installed but you need to push it straight and fairly hard and then it will go on farther and be secure.
+1 on what hog-doc said. I lost one cruising down I-75 towards Florida and stopped at Little River HD in Tifton, GA and bought a replacement. A tech installed it and I was surprised (shocked really) at how hard he pushed on the switch cap using the tuning fork-type tool for the install. He did the other audio, PTT and cruise caps as well. Totally different when he finished than what I'd done previously.