Yep, they rust from the inside out. This looked pristine half an hour ago, then I started using a wire brush.
Much of the car is not rusty, and I feel I can get a few more years out of it.
I found rocker panels at this placehttps://www.millsupply.com/auto-body-rust-repair-panels/subaru/ After I order the part, what's the next step? The rest of the car really is in great condition