Yes, I noted exactly the same over the winter. This trim, or fascia as HD call it, is secured by three nuts either side but is a push fit at the base into a bracket under the fender. After using Loctite glue to repair the crack, I packed out the base fitting and secured the nuts to eliminate any movement. With hindsight, I do remember watching that rear light unit wobble when the bike was ticking over on its side stand but thought it was just another Harley quirk. Basically, it's down to poor design and factory assembly.