Wow, good luck with that -- I gather that while these are not scarce in Exakta and M42 SLR mounts, the rangefinder versions are quite rare. And since they were made in Jena only, they have the wear-prone aluminum barrels, so finding a nice one could be harder yet.
Back before I knew anything about the rarity angle, I owned the LTM version for a while -- had bought it out of a "junk box" at a camera show, and it was in really rough shape, but still usable and with decent glass. I took some nice shots with it (one of which is in my RFF gallery.) A few years ago I happened to mention it on a photo mailing list, and got a reply from one of the big-name authorities in the field (someone who's written books on the subject) saying I must surely be mistaken, since only one or two examples of the LTM version of this lens were known to exist; I wrote back to him with serial number and photos, and he had to concede that I had the real thing!
That (plus stiff focusing and occasional inaccurate RF coupling) made me leery about using it, and eventually I sold it to the same expert (NOT for an exorbitant amount, mind you, since it was in such rough condition, but several times the $20 I had paid for it originally!) Some time later he wrote me back that it had required an expensive restoration, but with that done, the results were beautiful.
