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."
So basically it boils down to: