Well, I tried the 3-in-1 lock lubricant but the shade ring still won't come apart. I even heated the ring up with a hair dryer to see if I could get it to wick up into the threads. Tomorrow I'm gong to try some transmission oil. That's worked well in the past for me on frozen bolts. I've examined the shade ring closely and there's no visible distortion, dings, or cross threading. The lens came from a friend who took meticulous care of it. But I doubt he ever took the ring apart during the years he owned it. He shot mostly color film with it so all he ever did was remove the entire shade ring so he could screw on the polarizing filter.