That is exactly what I and everyone else thought, something not right about that left rear drum brake. The old guy said he had learned to drive the car without locking that wheel too often, that is until he tried to stop on snow. He did 360 degrees around through an intersection and was nearly hit. Scared the crap out of him. He left it with me and said find it and fix it no matter what it is.
I went to a parts yard and got booster and master from identical model. Of course I changed the booster first since I really don't like, trust, use, used master cylinders, plus I could change the booster without playing in brake fluid Booster didn't make any difference at all. The junk yard master cylinder fixed it.