Well, the Leica M is such a unique design that has its weaknesses but there is really no other option, so we have no choice but to put up with the quirks.
I have had a problem with the M9, the flaking sensor coatings, that was fixed by Leica for free. I have had a problem with the M(240), the baseplate was slightly loose, and also was fixed for free. I have not had any RF calibration problem with a new camera, and since I pamper my cameras against shocks, the RF so far always remained spot on.
Half of my ZM lenses came with less than optimal collimation, but that was also quickly remedied, and free as expected. I read on the forums that Leica and Voigtlander lenses also come with similar issues. That is the price to pay to shoot RF, but once everything works well, it is by far the most enjoyable and satisfying photo experience ever. It's well worth it.