I have a ZX-M. It was delightfully lightweight and small, carrying it around Bar Harbor, especially with the 40mm pancake lens on it. That said, its pricing would lead me to simply buy another rather than to have it repaired.
With a full line of Pentax lenses (and M42 mounts), the K series would be your best bet. I have two KX bodies. I've thought of replacing my ME Super, but the electronics can be hinky if they need repair. The K1000 is legendary. The KX has several more very desirable features for a mechanical camera. Funny how the market works: sometimes you can pick up a decent KX for less than a K1000. Give it some thought. (The K-series bodies are also good for self-defense.)
(Yes, I use all the old lenses with Pentax DSLRs, but I'm seriously thinking of going even further back in time and looking for an Asahiflex. It's pre-M42 mount, and would be a luxury acquisition, if I could find a good user.)