There has been some postings about Leica Custom Service, including from me, on these pages. Most of us tend to comment on things that are not fully agreeable, whereas more pleasant experiences are generally kept silent. So for the sake of balance, let me present a positive experience (and not the first one):
Three of my M-lenses needed focus adjustment (plus some repair/fixes). The package was received by Leica in early September. After a few days the initial screening was done and a cost estimate was sent to me. After additional 10 days the adjustments/repair was finished and returned.
Based on some initial testing the focus is now spot on for all of the lenses - which is clearly advantageous at f0.95 or f1.4 on a digital M...
The above is, perhaps, what to expect. I would nevertheless state that I'm satisfied with the turnaround time and the communication with Custom Service during the repair. Other brands might be quicker and/or have a better communication, but the opposite is possibly more likely.
Good.