Read a suggestion on another site to try dental floss to "degunk" under the bezel. Both my display back Cosmonaute and Old Navitimer bezels were so tight I could not move them at all without superhuman effort. Cut a long (10-12") length of dental floss, pushed the center of the strand under the bezel at one position and wrapped the strand around almost to where I started it. Pulled it around a couple of times and voila'! Worked great! The Navi bezel returned to its original (as I recall) perfect tension and the Cosmo bezel returned to its original tension as well. The Cosmo was always a bit tight but easily usable and it is again now. Give it a try. A very useful and easy technique for sure!
Cheers,
Ron