it might be the lens. but someone once told me to do it this way:
1. stand in front of a mirror.
2. set your lens to 1 meter focus
3. put a dot on the mirror with a marker or lipstick or something
4. with your lens focus set to 1 meter move forwards or backwards until the dot on the mirror is in focus.
5. then staying the same distance from the mirror, you move very slightly left or right and focus on the red dot of your leica.
6. then check the focusing on the lens – it should be at 2 meters. if not then the focusing it out of line.
You need a special tool to adjust your focusing on the M6’s and M7’s so if it is out of line then you’ll need to send it in to a repair shop.
I hope this helps.
Cheers,