Mind you, all my M42 lenses are 30+ years old and all work fine, but perhaps that is because they had been cared for in the past?[/QUOTE]

I have owned many of my M42 lens for almost 40 years, (bought my first body and lens set in 1969) and I have not taken any unusal measures to care for either the cameras mounts or lens, not one is even close to wearing out. I have dead meters but my camera bodies are still very solid and the lens are just as sharp as they were day I bought them.