Clutch shudder is a sometimes violent vibration when releasing the clutch pedal, and is generally worse when it is cold and damp. It can be attributed to a glazed clutch disk, a weak pressure plate, or condensation on the clutch disk face. It is generally a very difficult problem to replicate for the dealership, and not all dealerships will even acknowledge that it is a problem. The most effective way to prevent clutch shudder is to upgrade/replace the clutch disk and pressure plate. Of course, this is an expensive proposition if it is not covered by the factory warranty.