Unhappy Leslie imports 500 leather seats (7)
I believe the answer is:
saddles
'leather seats' is the definition.
'saddles' can be an answer for 'seats' (saddle is a kind of seat). I'm not certain of the 'leather' bit.
'unhappy leslie imports 500' is the wordplay.
'unhappy' becomes 'sad' (associated in meaning).
'leslie' becomes 'les' (short for Leslie).
'imports' is an insertion indicator (inserted letters are imported).
'500' becomes 'D' (Roman numeral for 500).
'sad'+'les'='sadles'
'sadles' enclosing 'd' is 'SADDLES'.
Can you help me to learn more?
(Other definitions for saddles that I've seen before include "Jockeys' seats" , "Burdens" , "Bicycle seats" , "Riders' seats" , "Riding seats" .)