I had this problem with the following cars:
8452 series Lackawanna;
8453 series New Haven;
8454 series NYC ( CCC&St.L);
8457 Series New York Central;
8461 Series New England Coal & Coke.
On all of these cars the center beam and the hopper doors disintegrated. Atlas provided free diecast replacement parts. Replacing the defective parts took quite a bit of effort. In the process some of the plastic detail parts were broken. I did not try to restore to like new because it was beyond my skill level.