First it is too broad a generalization to say Canon and Leica have the same lens mount. The original Canon thread mounts were 38.5mm x 1.1mm pitch and then true M39. Leica is NOT M39 because the thread pitch is not metric; it is 26 threads per inch. Leica should be called L39 because it is not M39. Canon switched to L39 in 1952. Leica thread mount was always L39.
So your 50mm f1.4 is L39 lens mount.
Now the question of the thread on the focusing mount in the lens. What has to be the same on all LTM and LBM lenses is the movement of the lens tab on the focusing cam. (I use the term "tab" even though on some Leica lenses it is actually a full circle tube.) Essentially the rangefinder doesn't know and doesn't care what focal length lens is mounted. It is just "solving" the triangle based on the two camera windows and the subject distance. The focusing pitch can be different for a given focal length as long as the focusing tab movement is the same for a given subject distance. On the 50mm Leica lenses, the back of the moving lens element (a full circle normally) bares directly on the focusing cam, so the pitch of the focusing mount has to be identical on all 50mm lenses. (There may be 50mm lenses that I don't know about for which this is not true. It is definitely true of the Canon 50mm 1.4) On longer focal length lenses the focusing mount has to have a steeper pitch because the glass has to move more to focus. On wide angle lenses the focusing mount has to have a shallower pitch because the glass has to move less to focus. It is hard to see on a wide angle lens, but the back focusing surface movement and the front of the lens do not move the same distance when focused. It can be easily examined with a caliper.
In control system terms the 50mm focusing mount has 0 gain. The telephoto focusing mount has negative gain. And the wide angle focusing mount has positive gain.
As an aside the Canon 0.95 is an example of a 50mm lens that has a tab instead of a full circle. But the movement is still 1 to 1.
Discussing further, the distance required to move a certain focal length to achieve focus is the same regardless of lens optical design. So the gain for a given focal length is the same regardless of the amount of rotation needed to focus the lens. You can have short throw and long through lenses based on focusing mount thread pitch, but the focusing tab movement has to be the same for a given subject distance.
Since these mechanical characteristics are machined into the lens, they are impossible to change. What is adjustable are: the focusing tab position by shimming the mount which is how a manufacturer accounts for small differences if as-built focal length; and the movement of the cam arms in the rangefinder. Also there is the possibility that the lens has been taken apart and reassembled incorrectly.
In my opinion, and it is just my opinion, the only way to check the lens shimming and the rangefinder adjustment with precision accuracy is with test equipment owned by a good camera repair shop. I don't feel that the rangefinder in the camera is accurate enough to check infinity focus. I know others in the forum regularly repair lenses and cameras without this equipment, but I feel that the best results are achieved with the equipment.
So my advice is to take or send the lens and camera reliable camera repair shop.
