Ok, took some pics while the seat is still in the car. It doesn’t show much, but I think the metal broke that the top rail bolts to. You can see the broken metal sticking out. Thinking I need the metal seat bottom.
So, the seat pan has rusted and the screw securing it to the seat rail has pulled out. Remove the seat cushion and inspect the seat pan. The cushions are held to the seat pans with some small metal tabs. Those need to be bent so they are straight down. Then, you can pull the seat cushion out.