Actually I haven't pulled the bezel assembly to look. I just noticed the lower part of the boot is flopping around loose underneath the bezel.
I've continued searching online (and the forum) and I'm just not finding anything about a fix for this apparently common problem.
Although it sounds a little cheezy, I wonder how well this would work...
Using the lower ring as a template, drill a series of small holes around the top of the bezel. Then use small panhead screw/bolts to literally bolt the lower ring to the underside of the bezel. That way even if the ring is cracked it would still stay in place.
Seems like it would work. I suppose if you used small enough hardware and painted the screw/bolt heads black it might look okay.
All the billet rings I find are just the upper trim piece, not a two part set - one above, one below - that would sandwich the edges of the boot in place.