Pictures of the groove?
Strangely, no manual I have ever read mentions this - which is strange because the bolt pattern is symmetrical, meaning you could overlook this step and still install the retainer in the housing...with predictably disastrous results!

... In the vid he shows it but just mentions it and moves on, and it looked like a somewhat flat disc with tangs on it at quick glance... That's what I kept seeing in my head lol