Question Author
Many thanks. aelmpvw. Very well spotted.
There are three possible 3-letter locations, the fourth already containing an L. In one of them, the first letter (1) is doubled elsewhere, so can't be an I. In another case, the immediately adjacent clue uses the same three letters and there's no such word so that possibility can also be ruled out. The one remaining possibility works fine. A word of caution: you need to use a Z where the obvious is a W.