I am located in Hong Kong and the repairman previously worked in Leica and he is retired now. It takes around 1 week for him to complete the calibration. Yes he did mention the same that the FLE is very tricky since it is only about focus shift it doesn't affect the "optical axis" not sure if this is the correct term. But yea this kind of calibration shouldn't be a big problem to them.
I know how you feel! because I had the same struggle, whole bunch of test shots and even doubt my eyes or my M10's rangefinder is off. If you tend to keep this lens, I strongly recommend you calibrate it because it is a great lens to keep!
Originally Posted by danieldouloslee
Thanks @anson0408 for that insight! Would you mind sharing how long/costly the process was? I'm keen on keeping the lens as it's probably something I'd never sell, but I want to make sure it is worth the unexpected added cost on my end. Surprisingly, YYE said he does not work on 50 lux ASPH given its complicated nature of the FLE.