One of the most important parts of the Voyager is apparently a little motor that rotates every 192 seconds to take 360 degree readings of the sky. Each rotation is called a "step" in their lingo .. they built it to run a few thousand steps (or about 4-5 years). And that little motor has now run over 5 _million_ steps over 48 years... and is still running.
More at https://www.nature.com/news/2008/080702/full/454024a.html