Some claim that the DS wind wears out faster than the Single Stroke wind because it sees twice as much action. I do not believe it. The main thing to watch out for in almost all Leica's (and most RF's) , especially older ones, is the RF patch going dim when the prisms/beamsplitters de-silver. This can be repaired, but figure on at least $200 if you get one with that problem. The shutter especially at lower speeds, can drag or "hang". I got by Leica M3 DS at a great price than had Essex CLA it and repair the finder for $220. The job had a two week turn-around, door to door, by getting an EMail estimate and including the check.
Also check with Youxin Ye EBAy seller wye7. He sells Leica gear that he has CLA'd. I have a very late user-condition Single Stroke from him that is so quiet you swear the shutter did not fire. The VF/RF is good on it, but not as perfect (like new) as what Essex did on the rebuild job. But then it cost a lot less.
