As an engineer things breaking down is pretty normal. I don't know a single machinery that hasn't eventually broken down even when being maintained well. The concept is simple the more it's used, the more likely it will break down. Sometimes the fix is easy but the majority of the time it needs a new parts replacement from the factory. Now the question is how would a space ship be maintained or fixed when it breaks down especially being worn down by light speed? Like I wrote before you can't just fix something on the spot without getting a parts replacement from the factory.