I am attempting to replace the nylon wheel at the end of the door regulator arm. The original is secured to the arm with a machined rivet head on one side and a large flat headed keeper on the other. I am not certain how they are joined together. I have attempted to turn the large flat head in hopes they are screwed together but no luck. What is the best method to separate the two heads and remove the old nylon wheel? Note in the pics that the flat headed keeper has a smooth shaft to which I will need to connect something to keep it in place. If I drill the old rivet head out, I am not sure what that will be. Help me please.