If any part of the device is not functioning properly, we replace it. However, we only replace the parts that do not work.
We do not use original Apple spare parts when replacing a part. We only use quality Original Equivalent Manufacturer (OEM) parts that have all passed our thorough quality control process.
This means that they are produced by a manufacturer that is certified to be of the equivalent standard as the original - the only difference being that the parts are not branded. They are often produced in the same factories, by the same people as the branded parts are.