And then when did the clapper itself break through metal fatigue? And how long did that repair take?
Search terms in various combinations:- Great Paul, bell clapper, repair, St Paul's.
Edit I've since discovered that Great Paul was silent from 1964, when they could no longer find a team of four men to swing the bell manually, until 1971 when an electrical system was installed. But this is not the period when the clapper was broken.