I had my corroded M9 sensor replaced in 2017 as part of Leica's free program.
Recently the camera died. I sent it to Leica NJ. They said there was nothing wrong with the camera, it just needed new batteries (mine are 10 years old) and I agreed to pay $265 for a CLA. A month went by. Today I received a new estimate saying that the 2017 sensor is corroded, asking for over $1,500 for the repair.
Until my M9 died, none of my pictures showed any evidence of sensor corrosion.
I called, and also wrote Leica, saying that if the sensor is in fact corroded, then the damage occurred at Leica. They agreed to have another technician look at the camera and will get back to me.
I hope it's an honest mistake on Leica's part. I cannot afford to upgrade.