I agree you need to take care of that ding first , then remove what left of your top cap , once you remove the top cap then you should b able to see the star nut ( which yes been around for 20 years or more, they were around before expander plug ) . If you unsure of the star nut it can be replace with a new one . The new one will push the old one down when install . As I stated before replace the star nut and the top cap and you should be fine .