In case you missed it there's a new firmware update for the C300. Make sure you choose the right version.
Link: http://www.usa.canon.com/cusa/professional/products/professional_cameras/cinema_eos_cameras/eos_c300#DriversAndSoftware
Link: http://www.usa.canon.com/cusa/professional/products/professional_cameras/cinema_eos_cameras/eos_c300#DriversAndSoftware
1. Enables the user to change fan operating mode between On and Automatic. When set to Automatic, the fan turns off during shooting at normal temperature. When the camera temperature rises, the fan starts automatically and lowers the temperature.
*EOS C300 only
2. Enables control of CINE-SERVO lenses using the RC-V100 remote controller.
3. Enables peripheral illumination correction for the following lenses:
EF lenses:
EF 16-35mm f/4L IS USM
EF-S 10-18mm f/4-5.6 IS STM
EF 400mm f/4 DO IS II USM
EF 11-24mm f/4L USM
EF 24-105mm f/3.5-5.6 IS STM
EF 100-400mm f/4.5-5.6L IS II USM
EF-S 24mm f/2.8 STM
CINE-SERVO lens:
CN7x17 KAS S/E1
4. When one of the following EF lenses is attached and power is turned off, the lens automatically retracts to its minimum length.
EF 40mm f/2.8 STM
EF-S 24mm f/2.8 STM
EF 50mm f/1.8 STM