Model superlatively lusty: most problematic (9)

I believe the answer is:

thorniest

'most problematic' is the definition.
(I've seen this before)

'model superlatively lusty' is the wordplay.
'model' becomes 't' (Ford Model T car).
'superlatively lusty' becomes 'horniest' (most horny).
't'+'horniest'='THORNIEST'

(Other definitions for thorniest that I've seen before include "Most troublesome or prickly" , "most problematic" .)

I've seen this clue in The Everyman puzzle in The Observer.

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