<After a hail damaged thousands of new cars parked in an open parking lot>

CEO: We need to repair and inspect each and every one. Our customers will get [a car/cars] that is/are in good working condition.

Which is correct?
...cars that are in good working...
If he had said "All our customers.." then he could have used "a car that is in good working order".
Thanks, Feebs. You are right. The article used 'a' with 'all our customers". Is there a rule that I'm not aware of?