Also from my Film Developing days, certain chemicals were one use only, but there was a piece of equipment I only ever used once
.... Those tongs for squeegeeing the water off a freshly developed film. Despite being brand new, the bloody thing obviously had some sort of dirt/dust on it, and it scratched an important film at the time!
What made it worse was they were small but substantial scratches, and it wasn't obvious what had happened until I came to print one of the pictures and I saw the enlarged image.
Straight to the bin for those!!