I have a self used M6 classic 0.72. The major scratches are the ones on the two sides as shown in the images. It is caused by the shoulder strap. Functionally, it works fine. I have used it last weekend. It has the original Leica case, but no manual.
This leather case shown in the figure is free. It was used for M3. I am not sure whether it works for M6. I didn't try it.
Ask for $1200 USD net to me.