On my WM9, I had difficulty with fitting the gen insert; It just wouldn't snap into the bezel ring, and glue wasn't an option I'd consider. Therefore, I replaced the entire bezel assembly- From the retaining ring to the insert. I'm pleased to say that the gen parts fit with zero hassle, but it did require more parts than I thought it would to get this done.
All said and done, the results have exceeded my expectations for this watch...
YMMV.