>>3477008only the chinese made ones from the '90s are affected by that problem. they started making the k1000 sometime in the '70s so there are probably millions of them out there just fine, before the production was moved to china.
early production japan made k1000 cameras have "Asahi" over the Pentax brand and the AOCo badge stamped on the prism housing. those are the "safe" ones to get, free from the prism corrosion issue. late hongkong and china made ones dropped that brandings.
you can actually fix it. just need to take out the prism and have the surfaces resilvered, though it migth be more economical to get another camera. there's some DIY silvering by alchemical magic videos on youtube so that's another alternative.
https://www.youtube.com/results?search_query=mirror+silvering 