I cannot help with the used LM-3S and further I understand that this RailPro user group forum. However, I also have an Atlas Classic GP-7 (from eBay) which I accidentally allowed a grandchild to reach and grab. Because the shell does not stay clipped on as designed, which I knew, the handrails were ripped apart and need to be replaced. There does not appear to be anything broken with the shell or frame, it just does not stay clipped on firmly. I tried a small dollop of Goop at the suggestion of a friend, but do not care for the results when having to open the shell again. Anyone have an alternative suggestion to keep the shell latched in place, or what may be wrong?