I doubt there is a perfect opposite of the saying a broken clock is right two times a day. But something that somewhat approaches it is:
Even Homer sometimes nods
idiom saying (also Homer sometimes nods, even Homer nods)
used to say that even an expert sometimes makes mistakes (Cambridge)
There is also this old saying:
“There are spots even on the sun” is an old proverb said to date back to the 18th century. It means that even the greatest, most important people still have their faults. (source)
I also came across thethis saying, which seems more appropriate for objects, compared to the two former ones which rather describe persons:
The best cart may overthrow.
But I only find it listed, never explained. See this A Complete Collection of English Proverbs, for example.