I have completed the grid and the instruction. I know it's not really necessary but I couldn't parse two answers - any help here would be gratefully received. (In both cases the wordplay leads to the answer and an extra letter.)
19a - Judge to be not pursuing concern (answer = reckon, extra letter = n.)
18d - Locally afoot, with moderation, to put to some purpose porter's dwelling (answer = gatehouse, extra letter = a.)