All cameras will probably fail eventually, but some are more fallible than others.....To summarize, in my long experience, anything electronic will prove troublesome sooner than their totally mechanical counterparts.......I won't even comment on the unreliability of digital gear!
My most reliable 35mm gear?......The earlier Nikons, my Nikon F still going strong, after over 40 years of use, only the mirror dampening foam has needed replacing. Much the same with my Nikkormat FT3 and later FM's. The last really reliable Nikon?...the FM2n in my opinion.
Least reliable?.....Apart from anything digital, Olympus OM's had a habit of jamming when used in conjunction with their (not very good) motor drive at the time. The flimsy cap covering the motor drive socket detached easily from the camera and got lost.
Earlier Canon's were good, F1's and Ftb's, later T90's not as strongly made..
Bear in mind I'm talking here about professional use, and systems I've had experience of.