Holes left behind from the manufacturer can rust if the OEM plugs fall out or is lost. Replace them with direct fit rubber grommets from 5.0 Resto. Choose from various size plugs to specifically fit each grommet hole in your Fox Body to keep the rust at bay. Pick them all up in a kit to get them all replaced at once. Shop Latemodelrestoration.com for any weatherstrip pieces you need for your 1979-93 Mustang.