Sounds like a bad chip to me. This is usually a blown mosfet for the motor power (as opposed to brakes).
How your retailer deals with it is a crap shoot. I'd be more inclined to send it to someone who can repair it, such as GregK, who offers that service, if you're not comfortable with Surface Mount soldering.
How it came bad is up for debate. They're old enough that it might be degradation... I'm assuming it was clear to you that it had never seen the inside of a slot car before (wires were untouched, no solder residue, etc)?
How your retailer deals with it is a crap shoot. I'd be more inclined to send it to someone who can repair it, such as GregK, who offers that service, if you're not comfortable with Surface Mount soldering.
How it came bad is up for debate. They're old enough that it might be degradation... I'm assuming it was clear to you that it had never seen the inside of a slot car before (wires were untouched, no solder residue, etc)?