In 1964 he jammed his pitching arm while diving back to second base to beat a pickoff throw. He was fine for his next two starts, but the morning after his second start he couldn't straighten his arm. The team doctor diagnosed "traumatic arthritis," a form of osteoarthritis caused by a traumatic injury. The doctor told him right then he would not have a long career. Some days his elbow blew up to the size of his knee.
I'm guessing Koufax wanted to pitch as much as he could while he still could. Maybe Alston sped up the problem, maybe it didn't.
After losing his final game to Palmer in the second game of the '66 World Series, reporters asked him what would have happened if his outfield hadn't committed the errors that allowed the O's runs to score. "We'd still be playing," was his response.