I have had a Super 23 for almost 25 years, but haven't used it much since I've found the Koni-Omega system more convenient in most respects.
Recently, I had occasion to get out the old Mamiya. I found that the plastic ring used
for locking the lens in place seems to be frozen; I can't turn it, and although I have used some extra mechanical assistance, I don't want to overdo it and break something. Am I forgetting something? Is there some simple pin allowing release of the ring which I'm overlooking, or do these things commonly become frozen with age?