Car’s attraction? Principal one overlooked (7)
I believe the answer is:
pullman
'car's' is the definition.
(Pullman is an example)
'attraction? principal one overlooked' is the wordplay.
'attraction?' becomes 'pull' (I've seen this before**).
'principal' becomes 'main' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'overlooked' suggests deleting specific letters.
'main' with 'i' removed is 'man'.
'pull'+'man'='PULLMAN'
(Other definitions for pullman that I've seen before include "Philip --, novelist" , "Luxury railway carriage" , "luxury car" , "Luxurious style of railway carriage" .)