I Had two ZM lenses 25mm and 5cm, I had no problem with either.
But there was detectable rotational play in both of the focus rings, this be easily felt and could just be seen visually. But did not vary in the 3-4 years I had the lenses, I bought them knowing it was there and they were both as new.
When I part exchanged them the dealer has the 25mm serviced cause he could detect the lube was drying out and the friction was uneven. He did not detect the play in the rings.
I sold them cause I found them too big/bulky, they were ok photographically.
The CV M and LTM lenses I have had have not had this or any problems, so I don't think it is build quality, rather Zeiss speciications.
I had wobble in my 35 ZM f2 Biogon. Zeiss USA serviced it. They were really cool. I really like the images from this lens. I would definitely buy Zeiss lens again. (The 'wobble' was mild play in left right direction, and manifested itself as a stiff focus action when lens focused in portrait orientation).
I too was plagued by the ZM wobble and I managed to fix it myself in half an hour, trying to spread the info:
I think I am similar to many here in having had a wobble and not knowing the full reason. I searched high and low on the internet and no-one seems to have opened one (or posted about it). I have a Zeiss zm 50mm 1.5 sonnar, this started to wobble. I left it wobbling and it got very bad indeed (3mm play on one corner!). The front element was solid as most people here.
I went to a local repair shop and was quoted an outrageous amount of money to fix it (over £200) so I took on the repair myself. Needless to say, half an hour later it was fixed.
The construction of the front is that the filter ring is held on to a plastic covered ring by 3 bolts. These are fine. The plastic covered ring however seems to manage to unscrew itself.
The hardest bit of the entire job is to get the cover ring out. Zeiss in their vanity chose to not put any dents etc in it to allow it to be gripped. I read on forums that one can use rubber to grip and turn the ring but mine was well stuck. It was however so loose I could grip it with some pliers without touching the glass. As can be seen, I did damage it slightly getting it out but its not something I am overly concerned with (I can appreciate others may differ). Having done this once, I think I could get it out without damage a second time...
My lower ring had two bolts completely undone. I removed them, applied loctite and tightened these. I cleaned the threads to the filter ring as well as the threads on the cover, sparingly applied moly lube to the cover threads and replaced this by hand (I want to be able to get the cover off more easily next time!).
The filter ring is now completely rock solid again :)
Some photos in time order, I hope they help others (documenting it has taken as long as fixing it did once I set to it):