I've used a 1600B for 4 years. It has worked well for me. I have not head much of anything form other users, on this forum, with any issues that had to do with ranging that required return to factory, etc.
It can get a little goofy when the battery starts to die and can get intermittent in its ability to range at all it seems.
Plus, all range finders can experience degraded performance due to bright sunlight, rain, fog, etc. It sometimes seem like the rangefinder, when it fact it is just environmental conditions at the time.
I would try to document the issues with their frequency, including range info and environment conditions. Try to make it repeatable, if possible. Then speak with Leica about it. They may just ask you to return it so they can test it out without much regard to the issues you experience . I have run into that with other service departments.
Good luck.