A few years ago, I bought a 4 pack of dark green Heavyweight passenger cars made by Lionel. The item number is 6-25713 and is from 2012.
After awhile of use, one of the coupler knuckles on the observation car had broken. So, I thought it would be a simple fix to replace, but when I picked up the car at the trucks, the entire truck seemed to crumble. The metal on the truck side frames broke EXTREMELY easily. From the side bar over the middle wheels to the VERY thin metal (that almost feels less strong than plastic) holding the rotating bearing caps.
Fortunately, I had some spare heavyweight trucks from a scrapped ATSF heavyweight from 2004 I had gotten for the StationSounds system. It was tedious to replace the truck, since taking apart these cars isn’t exactly easy, but the metal on those trucks proved to be far sturdier and robust. And of course a fresh knuckle coupler.
I know stories of zinc pest on train products tend to go around once in a blue moon, but if this a common case with the Lionel heavyweight passenger cars in the early 2010’s, I’d advise to keep your eyes peeled and check the ones you have...