Replacement parts are available for all of the GoPro range but I prefer to try and prevent any damage particularly when the camera and case are in my bag. One of easiest parts to damage is the lens of both the camera itself and the lens area on waterproof case. Damage to either of these will ruin footage.
The covers are made from a soft silicone material, come in a range of colours and work really well. They are also a quarter of the prices of the GoPro pack. These covers will fit the Hero 3+ and Hero 4 range.