Leading car brand announced: old Explorer (5,4)
I believe the answer is:
marco polo
'old explorer' is the definition.
(13th-century explorer)
'leading car brand announced' is the wordplay.
'leading' is a charade indicator (letters next to each other).
'car brand' becomes 'polo' (Volkswagen Polo).
'announced' becomes 'marco' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'polo' after 'marco' is 'MARCO POLO'.
Can you help me to learn more?
(Other definitions for marco polo that I've seen before include "Merchant of Venice" , "Traveller between 15 dn and 6 dn" , "Adventurous traveller" , "having month taking care of game" , "13th-century Venetian traveller" .)