Black spots were find on on photos with smaller aparture. It is unable to clean up. In the Leica users Forum, it tells it is a very common problem for Leica digital camera.
Quote from the Leica agent, products including camera and lenses are required to send back to Germany for servicing. Extra mailing cost and expensive service cost are faced. Also, it will take minimum over three months for the delivery.
No other choice, may be sent back to Leica to do the servicing after I buy the next body.