I have a NIB BB-UN72 left over from years ago and it looks like the outer shell was "turned over" the bearings at both ends, effectively locking them in. You would have to grind off the ends of the shell to free them. As noted, these were not designed to be serviceable and were replaced when worn out, which took a long time. If yours still turns smoothly and quietly, be thankful and keep using it until it doesn't.