A New Sensor, but Varying Notes
This is a late response to the original post, but I'm responding for others who might have a similar question and read this thread in the future.
A few weeks ago, I brought my Leica M9 to a store in Milan, near where I live, to have the image sensor cleaned -- they do that for free. I did this because there were several spots appearing on images. They kept it a few days and then told me the sensor needed to be replaced. They sent it to Leica in Wetzlar for me -- they didn't change me for the shipping cost either.
I received an email saying that they confirmed that the image sensor needed replacing and they would replace it for free -- which was very cool. They returned the camera to the Leica store in Milan after three weeks.
There were two letters accompanying the camera. One was entitled "Delivery Note". It mentioned working on the camera to include updating the firmware, adjusting the rangefinder, and cleaning. It did not say that they replaced the image sensor. The second letter included in the package was entitled, "Repair Invoice". On that one it says that the sensor was replaced and I was charged nothing.
To address your original concern, in my situation Leica did not say they replaced the sensor in one letter, but they did say it in the other. Plus, it looks like a different image sensor -- which could be my imagination -- there are no spots, and the firmware has been upgraded. Maybe you have one letter, but not the other.
Russell can be seen occasionally petting his Leica M3 camera and quietly calling it, 'my precious', much to the discomfort of those around him.
Russell's Photography Equipment (updated April 2015)
Leica M9 camera
Leica M3 camera
Leica Elmarit-M f2.8 21mm (E49) lens
Leica Summicron-M f2 50mm lens
Leica Elmarit-M f/2.8 90mm (E46 Germany) lens