Purely mechanical wear of the keyboard, which can cause a tactile sensation of looseness under the fingers, sometimes even a characteristic clunking sound, and visually, the keys appear to be falling to one side. This can also be caused by untimely detection of pests (moths).
The old felt trim is removed and a new one is glued in. It is also sometimes necessary to replace the polster, flakes, and washers, and to perform a "test run" and adjustment. The cost depends on the number of worn or damaged parts.