The first Seamaster 1948-9 Caliber 351 Bumper.
In 1989 this was handed to me in pieces, missing parts, second hand and the case covered in tar. I took it home, wound it up and left it overnight. It was running the next morning, so I set about cleaning the outer case, then took it to the local jeweler for assessment. He was able to find missing parts, crown (unsigned) a second hand (bit short) and new crystal. In the end it became a very wearable watch.
To this day, it keeps time +-5sec/day.