I was about to say the same. Normally German silver 3/4 plate gather patina, a yellowish tinge, and that enhances the beauty of the movement. I like it and it's not dirt at all. [nt]
This watch was serviced in 2017. Shall I be concerned or I could just wait until the next regular service? I assume Lange will be able to clean this? Is anyone encountering the same issue? Thank you for all your answers and advises!! Much appreciated!