The proper alignment of the optical system of an SLR is visual where in a Rangefinder the alignment is on good faith of the manufacturer or the last technician who worked on it.

Highly precise equipment will always be sensitive. The higher the quality of the output, the more
Precision Required of such a device, will often cause it to need more repair and adjustment and care in general. An Imacon film scanner for example needs adjusting much more frequently than an Epson V750, but the Imacon will do things the Epson won't. Rangefinders Are highly precise and require near perfect to perfect alignment of all parts of the system to function properly. If you need a rangefinder for the work you do, or prefer it ergonomic ally, or aesthetically, or for whatever reason, it's fickle nature is a necessary burden. I have dealt with many issues of collimating lenses and rangefinder alignment, but once you get a feel for your system and when it needs a checkup or may be "sick" you can stay ontop of the problems. A second body is helpful too.