All of a sudden, after 7 months of daily use of my Leica M11-P, the rangefinder patch got out of alignment at infinity. Additional, I could no longer focus properly even at shorter distances, which was particularly noticeable when shooting my Voigtländer Nokton 75mm f/1.5. Luckily, I found that this was easy to fix with just a 2mm Allen wrench, as demonstrated in the video below:
One of the commenters made the whole process even clearer, so I'm quoting it here: "As a guide for everyone, (with camera upside down so you can see) - anti-clockwise extends the throw of the RF patch when it has been stopping short, and clockwise brings the patch back when it goes too far."