Maybe they didn't dead head those cars to Willowbrook because there is no space in the shop. The article makes it sound like Alstom is negligent in some way but it could have been a defective batch of disks. Who knows. Maybe they used a cheaper bidder than usual?So only 4 of the 18 cars are in service. And they might be at risk as well.
I do wonder though how this is not as simple as simply replacing the brake discs.
Most of the fleet servicing the UP Express has been removed from operation after thermal cracks were discovered in the vehicle brake discs, according to the maintenance and operators’ union and confirmed by several sources, leaving Metrolinx with only four train cars in service for the rail link...toronto.ctvnews.ca