Sounds like gasket maker for sure between the snout and rotor plate, and also recommended between the rotor plate and casing.
Here'* a curveball. Say, while on the car, I want to occasionally remove the snout from the rotor plate without disturbing the seal between the rotor plate and casing. Is there something I could use between the rotor plate and casing that would form a stronger bond than gasket maker, but still seal that joint properly? (GM assembly adhesive, perhaps?)