The Z3 has to be my favorite shooter. Mine seems to have a good fit and finish, and they were made during the "golden days" of the FSU rangefinderdom. Many say that the slow speeds are unreliable on his model, but I find that mine was only unreliable because it was dirty. I spent a day or two inside mine to do a CLA, here is what I found I had to do:
1) Remove and clean the Slow speed delayer
2) Clean and lubricate wind mechanism
3) Clean and lube the slow speed mechanism at the top & bottom sections
4) Lowered the Curtain tension (They were waaay too tight)
5) Realigned the RF
6) Adjusted the Slow speed delayer and the stop for the "Time" exposure
7) Made a light seal for the back out of yarn.
It sounds like a lot of work...and it was. But, now that I have this smooth winding, relatively quiet Zorki with strap lugs and a nice bright VF, it was worth it. Everyone on this site can be very helpful if you need any help with it.