Looked at one of my Vito C's. And realized that the fixation of the lens assembly is not visible from the rear, being hidden by light shield 13801-38, see
If it were me, I'd separate the front plate from the camera body as shown on that page, and re-tighten the fixation of the lens (optics+shutter) to the front plate. You probably need to pay attention to various linkages that will need to be re-assembled properly:
- shutter cocking;
- shutter release;
- speed/aperture linkage to light-meter
Sorry I can't give you more specific advice, not having yet serviced a Vito Cxx