I think the M240 is inherently reliable as far as it goes.
But after thinking it over a little more I feel I should add this to my earlier post on this thread. I suspect the main problem anyone buying a Leica M240 is likely to experience is the same as the problem that every other Leica M have experienced or will experience eventually - the damned rangefinder which relies on wholly mechanical linkages goes out of specification, resulting in M lenses no longer focussing properly when mounted on that camera. I have read of some M shooters budgeting to send their camera back to Leica every year or 18 months to have this issue fixed. This problem can happen inexplicably even if the camera is molly-coddled and babied as mine tend to be. I had it happen to my M8 when going on a holiday - I suspect caused by nothing more than the camera sitting in my camera bag in a plane's overhead locker and experiencing the normal vibration that comes from a passenger jet flying from point A to point B. If you look this issue up on Google the posts about this kind of thing are many, if not legion.
Usually this requires a trip to a technician who knows what he is doing and hence there will be a cost and time spent without access to the camera.
At least I suppose the M240 has an alternative - the top mounted electronic finder - assuming you ante up another $400 for one. And while I am about it, I should mention that if your eyes are no longer 20:20 you will also need to pay for a diopter as Leica has never seen fit to try to engineer a Leica M finder with inbuilt diopter adjustment.
Though I was strongly tempted, several considerations did lead me, in the end, to buy a Leica Q instead of a Leica M240 when I decided to upgrade my Leica M8 a couple of years ago. Part of it was the autofocus available in the Q (combined with excellent MF) and its superb lens. But I think the above consideration was also at the back of my mind although not at the forefront of my decision making at the time. Having said all of this, as I said in my other post, I would still love an M240 for all of that. Damned Leica's they get under your skin.