All questions are answered by this email from the setter:
Thanks for your email.
Due to a production error, the last clue in Mephisto 2578, 28 Down, was omitted from both the paper and on-line versions. On the text file I sent, it was:
28 Look into publicity for old estate (4)
I will ask the Sunday Times to accept all otherwise correct entries, whichever of the two possible words that fit has been entered, or even if the relevant square hes been left blank.
All the best,