Hi, granama1,
For 30dn, the clue leads to a three letter word, which is a dialect word meaning “channels”, very popular in The Listener Crossword. The ordplay leads to the first three letters of a word meaning “rest”. The added letter in the entry is the second letter, which is given by 32ac, so the unchecked letter is the first letter of the original answer (which I assumed you already had).