The Royal Enfield Factory has issued an airbox retrofit that can be added to all C5 motorcycles prior to chassis number 508555.
The retrofit addresses the issue of the airbox door vibrating while the bike is being operated at half-open to wide open throttle settings. The retrofit also addresses the issue of unfiltered air entering the airbox housing around the hinge area of the airbox. It also precludes any pieces from a failed latch assembly from inadvertently getting into the engine via the intake air tube. The airbox insert takes only seconds to install with a 13mm socket and can be done by the service shop or by the owner of the motorcycle.
The retrofit will be available from your dealer ONLY, so give them a call to remind them if your chassis number is lower than 508555. It is expected that the dealer will do a "group order" for the inserts as they have all the VIN's for the bikes whose owners may want them. The insert won't take any performance away from the bike at all - BUT - if you have an aftermarket (read "taller") air filter in the can - the insert won't work. Tell your dealer that you need part number 591681 and BE SURE to give him your chassis number for his records.