Picture shows how I repair Atlas O rails when the small plastic retainer nub breaks. This can happen due to excessive stress when inserting rail joiners or sometimes just from forceful track cleaning. I cut small pieces of basswood, apply brown stain, and use epoxy to cement the basswood to the plastic tie. The edge of the basswood holds the rail down and in firm contact with the plastic tie. Seems to prevent separation of rail from tie. This repair is at least ten years old. You can see several such fixes in the picture.
MELGAR