They've all got parts that aren't feasible (or even reasonable) to replace. My Konica T3 has a failed light meter (like many of them). It would be $200 to fix, and the camera was $20 when I bought it. It's just a wire (and a tweak for modern batteries), but it requires disassembling 70% of the camera.
My GX680 is a great little(?!) camera, and I've said before if the CPU dies, it's dead. In reality, there's enough information in the service manual in terms of schematics, logic diagrams, signal diagrams, etc., that a capable team could design and build a replacement part. But it would be thousands of dollars.
Similarly, if Jay Leno's team can take a broken part from a Duesenberg, scan it into the computer, create a 3D model, fix the broken/worn aspect of the model, and produce a brand-new part on CNC equipment, then in theory, any mechanical part could be recreated. But the cost is prohibitive.