A while ago, Leica published some details about potential issues with the CCD sensors in their M series cameras. https://brown-family.org.uk/m9-ir-cover-glass-corrosion/
Until now if you had the issue Leica would replace the sensor with one from stock that potentially could have the same issue.
Well good news from Leica, they have announced they have developed a new generation CCD sensor for the M series and from now its these that will be fitted to Leica CCD rangefinders.
We are very pleased to inform you that we have successfully completed development on our new generation of CCD sensors and conducted subsequent quality assurance testing under practical conditions. As a result, Leica Camera AG can now begin replacing the sensors in the M9, M9-P and M-E models that were affected by corrosion with sensors from the new generation.
Sensor replacement for M Monochrom models will also begin shortly. We will inform you of the precise date of this as soon as possible.
On this note, we would like to remind our customers that we can only offer replacements for CCD sensors for cameras affected by this particular problem; prophylactic replacement is not possible.
We thank you for your patience and for your loyalty to the Leica brand.