Driver with case of wet rot turned back (8)
I believe the answer is:
motorist
'driver' is the definition.
(motorist is a kind of driver)
'with case of wet rot turned back' is the wordplay.
'with case of' is an insertion indicator.
'wet' becomes 'moist' ('moist' can be similar in meaning to 'wet'**).
'turned back' says the letters should be written in reverse.
'rot' reversed gives 'tor'.
'moist' placed around 'tor' is 'MOTORIST'.
(Other definitions for motorist that I've seen before include "Traveller" , "Car driver" , "One on the road" , "Car-driver" , "One driving" .)