I was visiting Marty Forscher's establishment in Manhattan so he could give my new M3 (recently handed down to me by my uncle who'd bought it in Germany in 1960) a lookover. After demonstrating the "L" seal to his acolytes, he asked me if my eyeglasses were being scratched by the eyepiece. When I said Yes, he then attached an "O"-ring he had handy to the eyepiece, and said, "There! Now you won't sctratch your glasses anymore." A fond memory.