I went ahead and bought the auto lens cap for Leica D-Lux 5. The cap is made of plastic but it fits well on the front lens thread (you will have to remove the protective ring first). The hinges are very loose but they do open and close smoothly when the lens extends/retracts. Using this cap will give you a fast response to sudden photo opportunities.
The cap can be purchased from eBay if you search for “auto lens cap Leica” or “auto lens cap Panasonic”. Here is a quick video of how it works:
Full list of all available auto lens caps after the break:
