At a previous employer (which will remain unnamed to protect the guilty), my team once discovered that we didn't have the source code for one of our production

At a previous employer (which will remain unnamed to protect the guilty), my team once discovered that we didn't have the source code for one of our production systems. Well, we had a version of the source code, but it wouldn't build. The version running in production? It was built on the workstation of a since-departed teammate, and apparently never checked into source control. Fortunately, the replacement for this system was already in development. Unfortunately, we had to patch the system on two occasions before its replacement was ready. Fortunately we were able to make both fixes by patching the binary - once to change a hard-coded encryption key that was linked in to the executable, and once to change a printf format string that was causing a critical bug in production. The day we finally launched the replacement system and retired the un-buildable codebase was the biggest relief of my career. (Not least because only the team and our immediate manager were ever told about the problem.)