You may be correct, but I'm less sure about this point -- but agree on the others in your list. Some original parts are getting more rare. You can buy new pre-B magazines from CZ, and the grip area can be opened up pretty easily so that new mags work.
I was a long-time participant and moderator on the CZ Forum and have owned a number of pre-Bs. I participated in a lot of discussions on this topic over the years and never heard of there being a problem with pre-B firing pins being damaged from dry-firing --
but my "not hearing about" the problem doesn't mean the problem doesn't/didn't exist... When I was active on that board -- about 10-15 years ago, pre-Bs were more talked about than seen.
The only firing pin problems I heard of were with the B-models, which use a firing pin retention roll pin to keep the firing pin in the slide. The roll pins would sometimes break from dry-firing. (I dry-fired a lot and only experienced that problem once, in a CZ-40B (which is basically very similar to the 75B except for grip design). A number of others has problems with broken roll pins, but they are easily replaced with a roll pin from a local hardware store, if cut to length.)
I've had a bunch of pre-Bs, and the only problem I heard of were some of the safety-lever-related issues with the early models, (like the one in the photo, with the hole in the lever). If you weren't careful when removing that lever (by putting a small screwdriver or pin in that hold to control the spring inside, the spring could go astray, and not be found. No replacement parts are available. Unhappily, the current safety lever mechanism is a different design and not compatible with the older frames, which lack the necessary detent fittings inside the frame to work.
One of my early CZs was very similar to the one in the photo, in original box, and if ever fired, it was fired very little. I also had several pre-B 85s in high-gloss blue (which very similar to the recently discontinued 85 Combat.) My second CZ was a pre-b, which had the original safety mechanism and enamel finish. I refinished it. That early model also didn't have the half-cock notch on the hammer. Years after I sold it, I found that it may have been one of the very rare "short rail" models (which didn't have the half cock notch.)
For the higher costs of a true low-mileage pre-B, I think I'd just get a good used B model, and send it off to Cajun Gun Works for David's improvements -- and end up with a gun that will be a joy to shoot, and has parts available if you ever need them. (That said, while parts are getting rare for some pre-B components, things just don't break that often.)
( I have a pre-B slide stop stashed away. I don't plan on having another pre-B so it will be sold, one of these days.
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