Factor30 clue which gave me the t in 23a is 19d:Fog(4) ?i?? (I had mist)
The clue which gave me the e in 23a was 18d: Entertain(5): a?u?? (I had amuse)
the clue which gave me the g in 23a was 7d: Deteriorating(13): r?t?o???s?i?? (i had retrogressing)