Complex sentence: A switch to their tiny Sports Coupé did the trick, and at age 60, he became German Hillclimb Champion for the last time; he decided to retire on a high note, and closed his professional driving career.
Split into simpler sentences: A switch to their tiny Sports Coupé did the trick, and at age 60, he became German Hillclimb Champion for the last time. He decided to retire on a high note, and thereupon closed his professional driving career.