I just got my black (circa 1984) Leitz 50mm Summicron M back from Malcolm Taylor, the UK Leica repair specialist and wanted to mention here what a superb job he did.
I wanted the lens 6 bit coded and a CLA done on it.
The 6 bit coding job was done to perfection.
In addition he has serviced the focus mount to remove play and improve focus, cleaned optics, fixed a problem with loose diaphragm and re-blacked the rear of the mount.
Very reasonable price and quickly done.
Previously I was having focus issues with the lens, it is such a delight now.
For those that do not know, here are Malcolm's details:
Upper Lye Farm
[I have no association other than a very satisfied customer].