thanks for the quick replies all.

For the eyepiece, I don't think any rubber has worn away. The eyepiece tube is part of the camera and has inside threads, so I'm pretty sure I'm missing a screw-in piece. As I understand it, the built-in diopter on old Nikons is -1, and the diopter eyepieces are rated for the overall diopter you will get after they are installed. So if I don't want to change the view, just have a rubber lip to protect my glasses from the sharp metal edge, I need to buy a -1 diopter eyepiece?