A833OD Aluminum Case - Part Of The Bearing Retainer Broke Off?

That's an overdrive right.
In the highest gear power actually goes down to the cluster first, then back up into the tiny overdrive gear. That means the front bearing is always working in that selected gear. Which means, as the bearing gets older, it gets noisy in overdrive, quieter in Direct/Third.

I've rebuilt a lotta lotta manual transmissions, but I've never seen a broken retainer like yours. Which makes me very curious.