Scooter treated with European wood preservative (8)
I believe the answer is:
creosote
'wood preservative' is the definition.
(I've seen this before)
'scooter treated with european' is the wordplay.
'treated with' indicates an anagram.
'european' becomes 'e' (abbreviation e.g. EU).
'scooter' anagrammed with 'e' can make 'CREOSOTE'.
(Other definitions for creosote that I've seen before include "Oily liquid obtained from tar" , "Wood preserver made from coal tar" , "Dark oily liquid, preservative for wood" , "Oily, smelly wood preservative" , "Wood-preserving oil" .)