Get Leica M Monochrom Typ 246 at B&H Photo.
My on-loan (production) Leica M Monochrom Typ 246 has two bad pixel columns (possibly more) which leads to image defects clearly visible with the subject matter containing parallel lines.
I reported the same type of issue with the Leica M9 in Sensor Defect: Bad Pixel Column (M9 CCD).
Bad individual pixels are unavoidable, and are routinely mapped out by camera firmware. Pixels can also be “killed” by cosmic rays even after the camera has shipped; this can be fixed by most vendors, again via a firmware update. Single bad pixels, even thousands of them (typical), are simply not an issue in a 24 megapixel sensor. But an entire bad pixel column has troublesome effects for the “wrong” subject matter.
Apparently Leica considers two entire pixel column defects to be acceptable, as seen here with the test camera (a production/release camera body). For such a high-end product, I have an expectation of getting quality commensurate with the price, and even more so for a specialty camera having no anti-aliasing filter. That means zero pixel column defects not two, or even one. Sensor costs do go up when rejecting sensors with bad pixel columns, but at around 2.5X to 4X the price of other full frame cameras, expectations for quality commensurate with the price is not unreasonable.
Together with the black spots issue, it might be wise to wait for some light to be shed on both matters by Leica.